Malondialdehyde oxidation of cartilage collagen by chondrocytes.

OBJECTIVE: The damage to cartilage collagen is a central event in the pathogenesis of cartilage aging and osteoarthritis (OA). We have previously developed an in vitro model of cartilage degradation which shows that chondrocyte-dependent lipid peroxidation mediates cartilage collagen degradation. The goal of our study was to investigate the role of vitamin C in this degradation model and to investigate effect of chondrocyte-dependent lipid peroxidation in the oxidation of cartilage collagen. METHODS: We studied primary articular chondrocytes. Effect of vitamin C was investigated in the previously described model. Serum-free stimulated and unstimulated chondrocyte-matrix extracts were subjected to SDS-PAGE and immunoblot analysis. Malondialdehyde (MDA)-protein oxidation of cartilage proteins was demonstrated by the reactivity of chondrocyte extracts to a monoclonal antibody, MDA2, which detects MDA-lysine adducts. RESULTS: Vitamin C treatment of chondrocyte cultures resulted in significant enhanced incorporation of 3H-proline label in cell-matrix. Cells treated with vitamin C, as compared to control untreated cells showed decreased spontaneous release of labeled matrix. Vitamin C treated or not treated chondrocytes responded comparably to stimulation with the agonist calcium ionophore A23187. The serum-free in vitro culture of chondrocytes resulted in MDA-protein oxidation. The treatment of chondrocytes with A23187 resulted in the enhancement of MDA-protein oxidation. The immunoblot reactivity pattern of extracts to MDA2 antibody and to polyclonal anti-type II collagen antibody was somewhat similar, which suggests that these two different types of antisera exhibit a crossreaction to chondrocyte proteins. Chondrocyte extracts were pretreated both with and without pure collagenase, and then subjected to immunoblot analysis. Only collagenase treated extracts showed a disappearance, or significant reduction, of larger than 60 kDa size MDA2 immunoreactive proteins. This suggests that the proteins that disappeared after the enzyme treatment were collagen proteins and which had also been modified by MDA oxidation. CONCLUSIONS: These observations suggest that collagen hydroxylation of matrix by vitamin C does not play a role in this model of chondrocyte-dependent collagen degradation. Also, this study demonstrates that chondrocyte-derived lipid peroxidation product MDA mediates oxidation of cartilage collagens. Oxidative modification of cartilage collagen in vivo could result in alteration of biochemical and biophysical properties of cartilage collagen fibrils, making them prone to degradation, thus initiating the changes observed in aging and OA.

Evidence linking chondrocyte lipid peroxidation to cartilage matrix protein degradation. Possible role in cartilage aging and the pathogenesis of osteoarthritis.

Reactive oxygen species (ROS) are implicated in both cartilage aging and the pathogenesis of osteoarthritis. We developed an in vitro model to study the role of chondrocyte-derived ROS in cartilage matrix protein degradation. Matrix proteins in cultured primary articular chondrocytes were labeled with [(3)H]proline, and the washed cell matrix was returned to a serum-free balanced salt solution. Exposure to hydrogen peroxide resulted in oxidative damage to the cell matrix as established by monitoring the release of labeled material into the medium. Calcium ionophore treatment of chondrocytes, in a dose-dependent manner, significantly enhanced the release of labeled matrix, suggesting a chondrocyte-dependent mechanism of matrix degradation. Antioxidant enzymes such as catalase or superoxide dismutase did not influence matrix release by the calcium ionophore-activated chondrocytes. However, vitamin E, at physiological concentrations, significantly diminished the release of labeled matrix by activated chondrocytes. The fact that vitamin E is a chain-breaking antioxidant indicates that the mechanism of matrix degradation and release is mediated by the lipid peroxidation process. Lipid peroxidation was measured in chondrocytes loaded with cis-parinaric acid. Both resting and activated cells showed constitutive and enhanced levels of lipid peroxidation activity, which were significantly reduced in the presence of vitamin E. In an immunoblot analysis, malondialdehyde and hydroxynonenal adducts were observed in chondrocyte-matrix extracts, and the amount of adducts increased with calcium ionophore treatment. Furthermore, vitamin E diminished aldehyde-protein adduct formation in activated extracts, which suggests that vitamin E has an antioxidant role in preventing protein oxidation. This study provides in vitro evidence linking chondrocyte lipid peroxidation to cartilage matrix protein (collagen) oxidation and degradation and suggests that vitamin E has a preventive role. These observations indicate that chondrocyte lipid peroxidation may have a role in the pathogenesis of cartilage aging and osteoarthritis.

Successful treatment of methotrexate induced nodulosis with D-penicillamine.

Accelerated nodulosis is a recognized complication of methotrexate (MTX) therapy in rheumatoid arthritis (RA). We describe 3 patients with accelerated nodulosis treated with D-penicillamine (D-Pen) while continuing MTX. The combination of D-Pen with MTX therapy resulted in regression of subcutaneous nodules in all patients, disappearance of pulmonary nodules in one patient, and resolution of vasculitic lesions in 2 patients. Clinical response was observed within the first few weeks of therapy and usually required moderate doses (500 mg/day). Our observations suggest that addition of D-Pen to MTX therapy can be an alternative therapeutic option for accelerated nodulosis in patients with RA.

Aggrecan degradation in chondrocytes is mediated by reactive oxygen species and protected by antioxidants.

Reactive oxygen species (ROS) are implicated in aging of cartilage and in the pathogenesis of osteoarthritis. However, the biological role of chondrocytes-derived ROS has not been elucidated. An in-vitro model was developed to study the role of chondrocyte-derived ROS in cartilage matrix degradation. The primary articular chondrocytes were cultured and the aggrecan matrix was radiolabeled with 35-sulfate. The labeled aggrecan matrix was washed to remove unincorporated label and chondrocytes were returned to serum free balanced salt solution. The cell-monolayer-matrix sensitivity to oxidative damage due to either hydrogen peroxide or glucose oxidase was established by monitoring the release of labeled aggrecan into the medium. Lipopolysaccharide (LPS) treatment of chondrocyte-monolayer enhanced the release of labeled aggrecan. Catalase significantly prevented the release of labeled aggrecan in LPS-chondrocyte cultures, suggesting a role for chondrocyte-derived hydrogen peroxide in aggrecan degradation. Superoxide dismutase or boiled catalase had no such inhibitory effect. The effect of several antioxidants on LPS-chondrocyte-dependent aggrecan degradation was examined. Hydroxyl radical scavengers (mannitol and thiourea) significantly decreased aggrecan degradation. A spin trapping agent N-tert-butyl-phenylnitrone (but not its inactive analog tert-butyl-phenylcarbonate) significantly decreased aggrecan degradation. Butylated hydroxytoluene also inhibited aggrecan degradation, whereas the other lipophilic antioxidant tested, propyl gallate, had a marked dose-dependent inhibitory effect. These data indicate that general antioxidants, hydroxyl radical scavengers, antioxidant vitamins, iron chelating agents, lipophilic antioxidants, and spin trapping agents can influence chondrocyte-dependent aggrecan degradation. These studies support the role of a chondrocyte-dependent oxidative mechanism in aggrecan degradation and indicate that antioxidants can prevent matrix degradation and therefore may have a preventive or therapeutic value in arthritis. The enhancement of oxidative activity in chondrocytes and its damaging effect on matrix may be an important mechanism of matrix degradation in osteoarthritis.

Hydroxyl radical formation in chondrocytes and cartilage as detected by electron paramagnetic resonance spectroscopy using spin trapping reagents.

Chondrocytes have been shown to produce superoxide and hydrogen peroxide, suggesting possible formation of hydroxyl radical in these cells. In this study, we used electron spin resonance/spin trapping technique to detect hydroxyl radicals in chondrocytes. We found that hydroxyl radicals could be detected as alpha-hydroxyethyl spin trapped adduct of 4-pyridyl 1-oxide N-tert-butylnitrone (4-POBN) in chondrocytes stimulated with phorbol 12-myristate 13-acetate in the presence of ferrous ion. The formation of hydroxyl radical appears to be mediated by the transition metal-catalyzed Haber-Weiss reaction since no hydroxyl radical was detected in the absence of exogenous iron. The hydroxyl radical formation was inhibited by catalase but not by superoxide dismutase, suggesting that the hydrogen peroxide is the precursor. Cytokines, IL-1 and TNF enhanced the hydroxyl radical formation in phorbol 12-myristate 13-acetate treated chondrocytes. Interestingly, hydroxyl radical could be detected in unstimulated fresh human and rabbit cartilage tissue pieces in the presence of iron. These results suggest that the formation of hydroxyl radical in cartilage could play a role in cartilage matrix degradation.

Posterior tibial neuropathy from ruptured Baker's cyst.

OBJECTIVES: To increase awareness of entrapment neuropathy caused by rupture of Baker's cyst. METHODS: A patient with psoriatic arthritis, ruptured Baker's cyst, and entrapment neuropathy is reported and the literature on this complication is reviewed. RESULTS: Nerve entrapment caused by rupture of Baker's cyst is rare. Neurological examination and demonstration of Baker's cyst by Color Doppler Duplex Ultrasound (CDDU) help in making the diagnosis. Nerve Conduction Study (NCS) may confirm the diagnosis of posterior tibial nerve entrapment. CONCLUSIONS: Peripheral nerve entrapment should be considered in patients with Baker's cysts and loss of sensation along the plantar aspect of the foot or other neurological symptoms or findings.

Bone cell behavior on Matrigel-coated Ca/P coatings of varying crystallinities.

Rat calvarial cell mitogenic behavior was investigated on various biomaterials coated with Matrigel, a basement membrane matrix containing growth factors. Low (20-40%) and high (70-90%) crystallinity hydroxyapatite (rHA and cHA), rough titanium (Ti), and tissue culture polystyrene (TP) surfaces were compared. Surface chemistry and calcium resorption of HA coatings, alkaline phosphatase activity (APA), and growth of cells were measured for Matrigel-coated and uncoated surfaces at 2, 7, and 14 days. Gene expression for four noncollagenous bone-related proteins (osteonectin, osteopontin, alkaline phosphatase, and osteocalcin) was also investigated by reverse transcription and polymerase chain reaction up to 28 days. Ca concentration in incubating solutions increased with time for the two types of HA coatings and was always greater for rHA than cHA. Surface chemistry and coating dissolution rates were not affected by the presence of Matrigel or cells throughout the study. APA of cells on the two HA-coated surfaces was comparably enhanced in the presence of Matrigel and was greater than on Ti surfaces. Only HA surfaces showed an increased APA of cells with time in the presence of Matrigel. Cell growth peaked at 7 days and was greatest for cells on the two HA surfaces and without Matrigel. At 14 days, cell growth was comparable on the four surfaces. The presence of HA and Matrigel enhanced cell-specific APA at 14 days. Gene expression for all four proteins investigated showed no differences between surfaces after 7 days. At 2 and 7 days, gene expression was indicative of proliferation for Ti, and of proliferation, differentiation, and mineralization for HA and TP more so without Matrigel. The addition of this matrix significantly enhanced mitogenicity of calvarial cells on HA only after 14 days. Matrigel eliminated differences seen between the two HA coatings. Gene expression was not enhanced or inhibited by the presence of Matrigel.

Development of fibroblast-seeded ligament analogs for ACL reconstruction.

We fabricated "ligament analogs" in vitro by seeding high-strength resorbable collagen fiber scaffolds with intraarticular (anterior cruciate ligament, ACL) or extraarticular (patellar tendon, PT) rabbit fibroblasts. Fibroblasts attached, proliferated, and secreted new collagen on the ligament analogs in vitro. Fibroblast function depended on the tissue culture substrate (ligament analog vs. tissue culture plate) and the origin of the fibroblasts (ACL vs. PT) PT fibroblasts proliferated more rapidly than ACL fibroblasts when cultured on ligament analogs. Collagen synthesis by ACL and PT fibroblasts was approximately tenfold greater on ligament analogs than on tissue culture plates. The composition, structure, and geometry of the collagen fiber scaffolds may promote collagen synthesis within ligament analogs in vitro. Ligament analogs roughly approximate the structure and strength of native ligament tissue. Ongoing in vivo studies suggest that autogenous fibroblast-seeded ligament analogs remain viable after implantation into the knee joint. With further development, ligament analogs may be useful as implants for ACL reconstruction surgery.

Posterior interosseous nerve entrapment in rheumatoid arthritis.

Posterior interosseous nerve (PIN) entrapment is a rare complication of rheumatoid arthritis (RA) which, together with extensor tendon rupture and metacarpophangeal joint dislocation, should be considered in the differential diagnosis of inability to extend the fingers. The inability to extend the thumb in PIN entrapment is a useful distinguishing clue on physical examination, and nerve conduction studies confirm the diagnosis. Elbow joint swelling and compression of the PIN at the arcade of Frohse are the main reasons for PIN entrapment in RA. Intraarticular steroid injections and surgical intervention resolve symptoms of PIN entrapment in RA. In our case, the addition of methotrexate, which induces a rapid antiinflammatory effect, resulted in resolution of weakness with complete recovery in the extensor muscles of the fingers.

Lucigenin-dependent chemiluminescence in articular chondrocytes.

We were recently able to measure intracellular levels of hydrogen peroxide within normal articular chondrocytes using the trapped indicator 2',7'-dichlorofluorescein diacetate. Further studies have shown that stimulated chondrocytes produce luminol-dependent chemiluminescence, suggesting that these cells produce hydrogen peroxide and singlet oxygen. In the present study, we have investigated the lucigenin-dependent chemiluminescence response in normal articular chondrocytes. Chondrocytes either in suspension or adhered to cover slips showed lucigenin-dependent chemiluminescence. There was a dose-dependent increase in chemiluminescence response when chondrocytes were incubated with soluble stimuli like phorbol-myristate-acetate, concanavalin A, and f-met-leu-phe. Catalase and the metabolic inhibitor, sodium azide, which inhibits the enzyme myeloperoxidase, had no inhibitory effect on lucigenin-dependent chemiluminescence production. Only the antioxidant, superoxide dismutase, prevented lucigenin-dependent chemiluminescence, indicating that this assay measures the production of superoxide anions by chondrocytes. We confirmed that chondrocytes release superoxide radicals using the biochemical assay of ferricytochrome c reduction. Since cartilage tissue is semi-transparent, we were able to measure chemiluminescence response in live cartilage tissue, showing that chondrocytes which are embedded within the matrix can also generate superoxide anion radicals. Reactive oxygen intermediates have been shown to play a significant role in the degradation of matrix in arthritis. Our previous and present studies suggest that oxygen radicals produced by chondrocytes may be an important mechanism by which chondrocytes induce cartilage matrix degradation.

Release of oxygen radicals by articular chondrocytes: a study of luminol-dependent chemiluminescence and hydrogen peroxide secretion.

We previously established that normal articular chondrocytes, like macrophages, express class II major histocompatibility antigens, present antigen, and induce mixed and autologous lymphocyte stimulation. In a recent study using the trapped indicator 2',7'-dichlorofluorescein diacetate, we were able to measure levels of intracellular hydrogen peroxide within normal articular chondrocytes (J Immunol 245:690-696, 1990). In the present study, we utilized the technique of chemiluminescence and the biochemical method of quantitating hydrogen peroxide release to measure the production of reactive oxygen intermediates by articular chondrocytes. Chondrocytes, in suspension or adherent to coverslips, showed luminol-dependent chemiluminescence that was dependent on the number and viability of cells. There was a dose-dependent increase in chemiluminescence in response to soluble stimuli, such as phorbol myristate acetate (PMA), concanavalin A (ConA), and f-Met-Leu-Phe (FMLP). Azide inhibited chemiluminescence, suggesting that the light emission in chondrocytes is myeloperoxidase dependent. The antioxidant, catalase, inhibited chemiluminescence but superoxide dismutase had no effect, suggesting that luminol-dependent chemiluminescence in chondrocytes mostly measured hydrogen peroxide. Chemiluminescence was also observed in fragments of live cartilage tissue, indicating that chondrocytes that are cartilage matrix bound can generate the respiratory burst response. Using the scopoletin oxidation assay, we confirmed the release of increasing amounts of hydrogen peroxide by chondrocytes exposed to interleukin-1, rabbit interferon, and tumor necrosis factor alpha. Tumor necrosis factor alpha had both priming and enhancing effects on reactive oxygen intermediate production by chondrocytes. Reactive oxygen intermediates have been shown to play a significant role in matrix degradation. We suggest that reactive oxygen intermediates produced by chondrocytes play an important role in the degradation of matrix in arthritis.

Tripeptide RGD-dependent adhesion of articular chondrocytes to synovial fibroblasts.

Cell-cell interactions play an important role in the development of cartilage. Heterologous and homologous cell-cell interactions are critical for chondrogenic differentiation during development. Cell-cell interactions in the formation of fracture callus and cartilage neoplasia also invoke the process of cartilage differentiation. We have investigated cell-cell interactions between articular chondrocytes and synovial fibroblasts and show that there was enhanced binding between these two cell types compared to background binding of the labelled cells to the tissue culture plastic surface. The binding of chondrocytes to fibroblasts was temperature- and calcium-dependent, suggesting ligand-integrin involvement. The peptide, GRGDSP, which competes with the ligand-integrin through the tripeptide RGD (arginine-glycine-aspartic acid), almost completely inhibited chondrocyte attachment to synovial fibroblasts. The control peptide, GRGESP, had no inhibitory effect on binding. Antibodies to fibronectin (Fn) inhibited chondrocyte attachment by about 50%. Monoclonal antibodies to the alpha and beta chains of the fibronectin receptor (FnR) interfered with the attachment of chondrocytes to synovial fibroblasts. A combination of antibodies to Fn and to FnR did not completely abrogate chondrocyte binding, suggesting that other ligand-receptors were involved in the adhesion process. Chondrocytes and fibroblasts were shown to express membrane-associated Fn and FnR, by immunofluorescence. The alpha and beta chains of FnR, migrating at 110 and 140 kDa, respectively, could be immunoprecipitated from [35S]methionine-labelled synovial fibroblasts and chondrocytes. Northern blots showed the presence of mRNA for the alpha and beta chains of fibronectin receptors in fibroblasts and chondrocytes. Changes in cell shape were observed in chondrocytes on attachment to fibroblasts, i.e. the chondrocytes appeared fibroblast-like, suggesting that the chondrocytes had dedifferentiated. These studies suggest that chondrocytes specifically bind to synovial fibroblasts through RGD-dependent receptors. beta 1 Integrins are involved in this adhesion process and these heterlogous cell interactions appear to have a negative influence on chondrogenic differentiation.

Articular chondrocytes secrete IL-1, express membrane IL-1, and have IL-1 inhibitory activity.

Previous work from our laboratory has shown that rabbit articular chondrocytes, like macrophages, produce reactive oxygen intermediates, express Ia antigen, and can mediate immunologic functions such as antigen presentation and induction of mixed and autologous lymphocyte reactions. We were interested in seeing if these cells could secrete interleukin-1 (IL-1) or express membrane form of IL-1 (mIL-1). Using the standard C3H/HeJ thymocyte assay, neither secreted IL-1 nor mIL-1 activity was detected in untreated or LPS-treated chondrocytes. However, the D10.G4.1 proliferation assay showed that chondrocytes, stimulated with LPS, secrete IL-1 and express the mIL-1 in a dose- and time-dependent manner. The IL-1 activity in LPS-stimulated chondrocyte supernatant and on fixed cells could be inhibited by anti-IL-1 antibodies. Sephadex G-75 chromatography of pooled, concentrated LPS culture supernatant resolved into two peaks of IL-1 activity at 13-17 and at 45-70 kDa, respectively. The bioactivity of chromatographic fractions were similar using both the thymocyte and D10.G4.1 bioassays. Western blot analysis of chondrocyte supernatant detects 17-kDa IL-1 beta; no processed 17-kDa IL-1 alpha was seen but IL-1 alpha-specific reactivity was observed at 64 kDa. Immunoblot analysis of chondrocyte lysates shows that cell-associated IL-1 is IL-1 alpha and is 37 kDa in size. PCR analysis shows the presence of mRNA for IL-1 beta and IL-1 alpha in LPS-treated cells; IL-1 beta mRNA was detected in untreated chondrocytes. The inability to detect IL-1 by the thymocyte assay is due to the presence of a chondrocyte inhibitor of IL-1 that can be demonstrated in cell sonicates, supernatants, and on paraformaldehyde-fixed chondrocytes. Chromatography of LPS-stimulated supernatant showed a peak of IL-1 inhibitory activity at 21-45 kDa. Chondrocytes which secrete IL-1 and express mIL-1 could play a critical role in maintaining chronic inflammation in rheumatoid arthritis. Therefore, the ability of chondrocytes to produce both IL-1 and an inhibitor to IL-1 is important in interpreting the mechanism of cartilage matrix maintenance and degradation.

Production of hydrogen peroxide by rabbit articular chondrocytes. Enhancement by cytokines.

Recent evidence suggests that reactive oxygen intermediates may play a role in the etiology of cartilage matrix degradation in arthritis. We have previously established that normal articular chondrocytes can functionally act as macrophages. These functions include expression of class II MHC Ag, presentation of Ag and induction of mixed and autologous lymphocyte stimulation. Inasmuch as the production of reactive oxygen intermediates is a hallmark of macrophage activity during inflammatory response, we were interested in examining the ability of normal articular chondrocytes to produce reactive oxygen intermediates. Using the trapped indicator 2',7'-dichlorofluorescin diacetate (DCFH-DA), we measured the levels of intracellular hydrogen peroxide within normal rabbit articular chondrocytes. We found that Concanavalin A induces chondrocytes to rapidly oxidize 2',7'-dichlorofluorescin diacetate to a highly fluorescent dichlorofluorescin in a dose- and time-dependent manner. Fluorescent dichlorofluorescin oxidation by chondrocytes was inhibited by the addition of catalase, an enzyme that detoxifies hydrogen peroxide. Exposure of rabbit chondrocytes to either IFN-gamma or TNF primed the chondrocytes to produce significantly greater amounts of hydrogen peroxide with or without further stimulation. Using scopoletin oxidation as a measure of the release of hydrogen peroxide, we confirmed that chondrocytes released this reactive oxygen intermediate after adherence to serum coated culture plates. Rabbit articular chondrocytes produced and released greater amounts of hydrogen peroxide than pulmonary alveolar macrophages, a well characterized macrophage cell type. These observations suggest that chondrocytes are an important source of reactive oxygen intermediates. Furthermore, the production of reactive oxygen intermediates by chondrocytes may be an important mechanism by which chondrocytes induce structural and functional alterations in cartilage matrix observed during arthritis.

Secretion of plasminogen activator by cerebral astrocytes and its modulation.

Plasminogen activator (PA) has been related to the neuron migration during brain development. PA has also been shown to degrade myelin basic protein. We present data to show that neonatal Balb/c astrocytes show PA activity on 125I-fibrin coated plates. Secreted and cell associated fibrinolytic activity is detected only in the presence of plasminogen. Modulants like concanavalin A and phorbol myristate acetate enhance PA production and this function involves a transcriptional event. Dexamethasone inhibits baseline as well as concanavalin A induced enhancement of PA activity. These results raise the possibility that astrocytes may have an active role in myelinoclastic disorders and CNS developmental defects.

Characterization of astrocyte plasminogen activator.

We have previously shown that astrocytes produce and secrete plasminogen activator (PA) and that this function is responsive to various modulating agents. When astrocyte conditioned medium (CM) is subjected to SDS-PAGE and PA activity localized by fibrin-agar gel overlay, the activity in the CM is found to comigrate with control t-PA. On affinity chromatography CM PA specifically binds to t-PA antibody. The latter also inhibits fibrinolytic activity of CM PA. When incubated with a fibrin clot, CM PA activity can be shown to bind to fibrin. These observations help identify the enzyme in astrocyte CM as t-PA. A possible role of astrocyte PA in myelin injury could provide an explanation for the previously observed correlation between fibrin deposition and demyelination as well as inhibition of demyelination by ancrod and heparin in experimental allergic encephalomyelitis.

Normal human neutrophils are a source of a specific interleukin 1 inhibitor.

In the course of our study on neutrophil production of an interleukin 1 (IL-1)-like factor, we found that the addition of polymorphonuclear neutrophils (PMN) to monocytes cultured in the presence of zymosan resulted in decreased IL 1 activity of the resultant supernatant, suggesting that PMN may contain an inhibitor of IL 1. The objective of this investigation was to study this IL 1 inhibitor which normal human PMN contain. The inhibitor is constitutively present in the PMN because 0 hr PMN lysates and unstimulated PMN supernatants also show inhibitory activity. The PMN inhibitor inhibits IL 1 (crude and partially purified) in a dose-response manner and does not affect basal [3H]thymidine incorporation in the presence or absence of PHA-P. The PMN inhibitor does not have any effect on interleukin 2 (IL 2)-induced proliferation of the IL 2-dependent CTLL cells. The inhibitor can be generated in the absence of serum and is not produced as a result of proteolytic activity from PMN enzymes. The inhibitor is heat-labile and is most stable at neutral pH. Gel filtration studies on Sephadex G-200 indicate that the inhibitor is heterogeneous in size. Two inhibitory peaks, at 45,000 to 70,000 m.w. and at greater than 160,000 m.w., were observed. When zymosan-stimulated PMN supernatant was chromatographed, there was separation of inhibitory factor from a 17,000 m.w. proliferating factor. Presence of this PMN inhibitor may be important in negative regulation of IL 1.

Interleukin 1 production by human polymorphonuclear neutrophils.

The purpose of this study was to determine whether human polymorphonuclear neutrophils (PMN), which share a common cell lineage with macrophages, could produce factors such as IL 1. Other properties which these two cell types share are their phagocytic nature and the common receptor and antigens on their cell surfaces. IL 1, in many of its physical, biochemical, and functional characteristics, is found to resemble endogenous pyrogen (EP). PMN have been cited as a possible cell source of EP, but there have also been reports in which the capacity of PMN to produce EP has been questioned. This study shows that normal human PMN can be stimulated by particulate agents such as zymosan and soluble agents such as phorbol myristic acetate to produce a factor(s) which induces proliferation of mouse thymocytes, i.e., PMN IL 1. This PMN IL 1 was released from PMN in a dose- and time-dependent fashion. PMN IL 1 was nondialyzable, was heat-labile, and was inactivated at pH below 5 and above 8. PMN IL 1 stimulated the proliferation of normal human synovial fibroblasts and caused release of a neutral protease (plasminogen activator) from synovial cells. The synovial and thymocyte-proliferating capacity of PMN IL 1 was not affected by the protease inhibitor aprotinin or by soybean trypsin inhibitor. Gel filtration studies estimate the m.w. of PMN IL 1 to be approximately 13,000 to 17,000.

Class II histocompatibility antigen-mediated immunologic function of normal articular chondrocytes.

Using monoclonal antibodies, we examined the display of rabbit Ia by articular chondrocytes. We found that 29 to 46% of chondrocytes displayed Ia antigen compared with 46 to 60% of spleen cells. Ia antigen expression was not likely to be the result of enzyme treatment. To investigate antigen presenting activity of enzyme dissociated normal articular chondrocytes, adult rabbits were immunized in the front foot pads with ovalbumin (OVA) in complete Freund's adjuvant. Four to six weeks later, draining popliteal lymph node cells (LNC) were obtained. Articular chondrocytes were obtained by overnight collagenase, DNase, and hyaluronidase digestion of cartilage from both ends of femurs and proximal end of tibias. Antigen-presenting cells from spleen were used as positive controls. LNC and nylon wool-purified T cells were cultured with OVA pulsed and mitomycin C-treated chondrocytes or spleen cells, and lymphocyte proliferation was measured by 3H-TdR uptake. Both chondrocytes and spleen cells showed antigen presenting activity, and stimulation of lymphocyte proliferation was inhibited by murine monoclonal anti-rabbit Ia antibody (2C4), whereas control plasmacytoma cell supernatants had no effect. When T cells were purified first by Sephadex G-10 and later by nylon wool columns, these cells were dependent on antigen-presenting cells for immunogen (OVA)-induced lymphocyte proliferation. Again, chondrocytes under these strict experimental conditions presented antigen to T cells. Chondrocytes also stimulated autologous and allogeneic normal lymphocytes. Thus, normal chondrocytes have Ia antigens on their surface and can function as antigen-presenting cells. These results are significant for the understanding of local cellular interaction in the pathogenesis of rheumatoid arthritis.

Macrophage-related fibrinolysis in experimental disseminated histoplasmosis.

A model of disseminated histoplasmosis in CBA/J mice was developed. Cultures of Histoplasma capsulatum from the spleens of infected mice suggested almost complete clearance of fungi by week 3. The adherent spleen cells from infected mice showed a 2- to 20-fold increase in fibrinolysis. The increase in activity was maximal around 1 to 2 weeks and disappeared after week 3 of infection, and this paralleled the progressively decreasing number of culturable fungi from the spleen. In vitro coculture of infected spleen cells or nylon wool-purified immune T cells and proteose peptone-induced macrophages resulted in increased fibrinolysis. Peritoneal exudate cells from infected mice also showed increased fibrinolysis. The addition of soluble antigen to an in vitro culture system resulted not only in an increase in fibrinolytic activity of peritoneal exudate cells derived from infected mice but also of proteose peptone-induced macrophages. These observations suggest that spleen and peritoneal macrophages from H. capsulatum-infected mice exhibit increased fibrinolysis which in turn is indicative of macrophage activation. The mechanism of activation occurs as a result of immunologically specific T cell-macrophage interaction and by the action of histoplasma products on the macrophages. The significance of these findings and the role of the plasminogen activator assay in studies of disseminated fungal infection are discussed.