gp120- and TNF-alpha-induced modulation of human B cell function: proliferation, cyclic AMP generation, Ig production, and B-cell receptor expression.

BACKGROUND: It is well known that HIV-1 infection induces profound alterations in the immune system, including hyperactivation of B cells. TNF-alpha induces HIV-1 replication and immunodysregulation, including polyclonal B-cell activation. OBJECTIVE: We sought to determine the effects of surface-binding HIV-1 envelope glycoprotein (gp120) and TNF-alpha on human B-cell function. METHODS: HIV-1 seronegative peripheral blood human B cells were purified and activated by CD40 mAb and IL-4. In vitro studies of B-cell proliferation, cyclic AMP (cAMP) generation, receptor expression, and Ig production were performed. RESULTS: gp120, an Ig superantigen, stimulated HIV-1 seronegative and HIV-1 seropositive human B-cell cAMP generation, proliferation, and Ig production. These gp120-induced B-cell responses were demonstrated to be specific as evidenced by the abrogation of the stimulatory response in the presence of anti-gp120 mAb, blocking of CD4 resulting in no change on gp120-induced B-cell responses, and the binding of gp120 in these B cells. TNF-alpha also stimulated cAMP generation, proliferation, and Ig production in B cells, and the binding of gp120 to these B cells stimulated by TNF-alpha further enhanced cell proliferation, cAMP generation, and Ig production. Antigenic expression of the B-cell receptor CD79b was down-regulated by gp120 but was not altered by the addition of TNF-alpha. CONCLUSION: gp120 modulation of TNF-alpha-induced B-cell receptor- and cAMP-mediated signal transduction events may be involved in the B-cell abnormalities observed in HIV-1 infection.

Differential effects of interleukin-2 and interleukin-4 on immunomodulatory role of platelet-activating factor in human B cells.

Platelet-activating factor (PAF), a naturally occurring phospholipid cytokine, is a potent mediator of allergic and inflammatory reactions, as well as a modulator of immune responses. In the present study we showed that PAF is involved in early B-cell activation, as demonstrated by the increased cyclic AMP (cAMP) generation by PAF in a time- and dose-dependent manner in anti-mu antibody- plus B-cell growth factor-activated normal human peripheral blood B lymphocytes. PAF also regulated differentiation by causing a biphasic response on immunoglobulin M (IgM) production with an inhibitory signal generated at 10(-6) M and a stimulatory signal generated at 10(-8) to 10(-10) M. PAF enhanced IgA secretion. The regulation exerted by PAF was shown to be specific because the addition of the PAR antagonist CV-3988 abrogated these effects and the inactive form of PAF, lyso-PAF, induced neither cAMP generation nor immunoglobulin secretion in normal human B cells. Other cytokines, interleukin-2 (IL-2) and IL-4, potent mediators of the immune response, were unable to elicit a cAMP response in B cells. However, the addition of PAF (10(-6) M) with wither IL-2 or IL-4 enhanced cAMP production above the levels enhanced by the addition of PAF alone. IL-2 or IL-4, individually, stimulated IgM production, yet costimulation with PAF resulted in a differential effect between IL-2 and IL-4. PAF down-regulated the IL-4-induced IgM secretion, whereas the IL-2-induced IgM secretion was enhanced. The presence of CV-3988 returned all valued to those obtained with IL-2 or IL-4 alone, demonstrating the specificity of PAF. These data suggest that PAF is an important B-cell immunomodulator which can interact with other leukocyte cell mediators.

Isolation and culture of rhesus monkey pancreatic ductules and ductule-like epithelium.

The objective of this work was to devise methods for the isolation and culture of duct epithelium from rhesus monkey pancreas with the expectation that such methods would be applicable to the human pancreas. This objective is important because of the role duct epithelium appears to play in human diseases such as pancreatic cancer and cystic fibrosis. Pieces of freshly procured pancreas were minced and enzymatically dissociated, resulting in a digest that contained a few isolated ductules (intralobular ducts) as well as numerous small tissue fragments consisting of roughly equal proportions of ductular and acinar cells. These fragments were suspended in a rat tail collagen gel and cultured for up to 2 weeks in a medium supplemented with cholera toxin, epidermal growth factor, and other additives. A few cystic ductular fragments were initially observed among a large number of predominantly solid fragments. Later, most of the solid fragments also became cystic and eventually resembled the ductules except for being spherical. Autoradiographic analysis of DNA synthesis showed that the cysts possessed a proliferative potential. The cysts consisted almost entirely of ductule-like epithelium with no recognizable acinar cells, and exhibited greatly reduced concentrations of the acinar marker enzymes amylase, chymotrypsin, and gamma-glutamyl transferase. In contrast, the specific activity of the duct marker enzyme carbonic anhydrase was elevated in freshly isolated digests compared with the whole pancreas and this elevated activity was maintained for 4-5 days of culture, after which it declined. Other evidence for the ductular nature of the cysts was their low density relative to freshly isolated acinar tissue, their ability to distend (suggestive of fluid/electrolyte secretion), and the accumulation of mucins at the apical borders of the cells. The results show that fragments of rhesus monkey pancreas that are enriched in ductular epithelium assume some of the properties of ductular cells when cultured in a collagen gel. These epithelial preparations should facilitate biochemical and physiological studies of this important pancreatic cell type.

Cyclic AMP-mediated modulation of immunoglobulin production in B cells by prostaglandin E1.

We had previously demonstrated in a transformed human B cell line, LA350, the existence of an inverse relationship between cyclic adenosine monophosphate (cAMP) content and immunoglobulin secretion using the cAMP-elevating agents such as cholera toxin and forskolin. In this paper we report that cAMP acting as a second messenger for prostaglandin exerts a similar effect on the antibody response of B lymphocytes. Incubation of the cells with PGE1 in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) produced a concentration- and time-dependent elevation of intracellular cAMP. Significant increases of cAMP production were observed at physiologically relevant levels of PGE1 (10(-7) and 10(-8) M). Immunoglobulin production, whether measured as the total number of immunoglobulin-secreting cells by a reverse hemolytic plaque assay or as specific immunoglobulin production (IgM) by an enzyme-linked immunoadsorbent assay, was suppressed in a dose-dependent fashion by the presence of IBMX. This suppression of immunoglobulin production was significantly enhanced by the presence of PGE1. Phorbol myristate acetate-induced IgM production was also inhibited by the presence of PGE1. These results imply that prostaglandins regulate B cell activation and immunoglobulin production by signal transduction mechanisms involving cyclic nucleotides.

Enhancement of cyclic AMP metabolism in a B cell line by protein kinase C.

In a human B cell line in which we previously demonstrated an inverse relationship between cyclic adenosine monophosphate (cAMP) content and immunoglobulin secretion, the phorbol ester, phorbol myristate acetate, (PMA), was shown to augment the cAMP elevating ability of cholera toxin (CT), suggesting a regulatory linkage between the two transmembrane signaling pathways, cAMP and phospholipid (J. Immunol. 141, 1678-1686, 1988). We now extend these studies and provide additional evidence that activated protein kinase C, a principal product of the activation of the hydrolytic phospholipid pathway, plays a direct role in the augmentation of cAMP levels in cells stimulated by diverse cAMP-elevating ligands. Prostaglandin E1 (PGE1), forskolin (FSK) and CT, all of which demonstrated a concentration and time-dependent elevation of intracellular cAMP, produced even greater (up to twofold) elevations of cAMP in the presence of PMA or the diacylglycerol analogs, 1,2-dioctanoylglycerol (DiC8), and 1-oleoyl-2-acetylglycerol (OAG). In the absence of CT, PGE1, or FSK, these protein kinase C activators produced only small increases in cAMP content of the cells. Several tests of protein kinase C specificity in these PMA-, DiC8-, and OAG-induced augmentations were made: (i) only phorbol esters known to activate protein kinase C worked, (ii) PMA augmentation was abolished by down-regulation of protein kinase C, (iii) Staurosporine (a known inhibitor of protein kinase C) selectively inhibited the effects of PMA on cAMP generation and on immunoglobulin secretion in the LA350 cell line.

Rat pancreatic interlobular duct epithelium: isolation and culture in collagen gel.

Interlobular duct fragments from the pancreas of the rat were isolated by collagenase digestion and filtration, embedded in a matrix of rat-tail collagen, and cultured in a 1:1 mixture of Dulbecco's minimal essential and Ham's F12 media supplemented with cholera toxin (CT, 100 ng/ml) and epidermal growth factor (EGF, 10 ng/ml) in addition to supplements used previously, thereby improving the yield of ducts by a factor of two compared with previous results. The ducts were harvested by digestion of the collagen matrix with collagenase and were then dissociated by treatment with EDTA in divalent cation-free salt suspended in collagen and cultured as were the ducts. Numerous cysts appeared as a function of time and some of these enlarged dramatically. Some of the larger cysts exhibited secondary tubular processes extending into the surrounding collagen. The addition of bovine pituitary extract (BPE, 50 micrograms/ml) doubled the number of cysts, whereas omission of serum or CT + EGF reduced the number. BPE or forskolin could substitute effectively for CT. Agents that stimulate (secretin) or inhibit (e.g., ouabain or acetazolamide) fluid-electrolyte secretion in vivo had no effect on the number or average diameter of the cysts. The cysts were 83 to 88% epithelial with the balance of the cells being fibroblastic in appearance. Some cysts consisted only of epithelium. The proliferative capacity of the cystic epithelium was shown by the presence of mitotic figures and by an autoradiographic labeling index of 22 to 30% after a 24-h exposure to [3H]thymidine. The labeling index was reduced by the omission of CT + EGF. Transmission electron microscopy showed that the cysts exhibited morphologic features of duct epithelium in vivo, including apical microvilli, lateral interdigitations of the plasma membrane, and typical cytoplasmic organelles.

Modulation of a human lymphoblastoid B cell line by cyclic AMP. Ig secretion and phosphatidylcholine metabolism.

A transformed human B cell line, LA350, was found to be sensitive to cAMP-elevating agents by responding with rapid (0 to 2 h) severalfold elevations of intracellular cAMP to treatment with cholera toxin, isobutylmethylxanthine (IBMX), forskolin, and dibutyryl cAMP (all p less than 0.001). These cAMP-elevating agents also produced significant inhibitions of subsequent (48 to 72 h) Ig secretion by the same B cells as measured by a reverse hemolytic plaque assay and an enzyme-linked immunoadsorbent assay for IgM (both p less than 0.001). PMA- and IBMX-treated cells were particularly responsive to the effects of cholera toxin, showing a doubling of cAMP content and profound decrease in Ig production (p less than 0.001). Because our previous studies had correlated activation of the metabolic turnover of the phosphatidylcholine (PC) fraction of membrane phospholipids with enhanced Ig secretion, we examined the sensitivity of PC metabolism to cAMP in control and PMA-stimulated cells. Formation of PC was found to be inhibited by forskolin and IBMX (both p less than 0.002) but breakdown of PC was stimulated (p less than 0.001). These findings imply that as the enzymatic products of PC, choline phosphate and diacylglycerol, are depleted due to the combined effects of cAMP upon synthesis and turnover of PC, there is a decrease in Ig secretion. Since diacylglycerol activates protein kinase C, it appears reasonable that Ig secretion is at least partially regulated by cAMP-responsive alterations in PC metabolism produced by protein kinase C-induced phosphorylation. We conclude that the early cAMP-sensitive changes in PC metabolism in this activated B cell line may signal for subsequent alterations in Ig secretion.

Biochemical and histochemical characterization of cultured rat and hamster pancreatic ducts.

Pancreatic duct fragments were isolated from rat and hamster pancreas and were cultured in an agarose matrix for up to 8 weeks (rat) or 20 weeks (hamster). The fragments consisted predominantly of duct epithelium, lesser numbers of stromal and atrophied acinar cells, and small numbers of islet cells. Hamster ducts averaged 3 micrograms protein per duct while rat ducts averaged 1 microgram, and the protein:DNA ratio of both types of ducts was less than that of whole pancreas. Estimated average duct yields of 6% (hamster) and 1% (rat) were based on the protein content of the ducts. Duct viability was shown by the incorporation of 3H-thymidine and 3H-leucine into bulk DNA and protein and by autoradiography. gamma-Glutamyl transferase and (Na + K)-ATPase specific activities were slightly elevated while amylase was depressed in the ducts when compared with whole pancreas in both species. gamma-Glutamyl transferase was localized histochemically in both duct epithelium and in surviving acinar tissue, as seen in vivo. Amylase was shown by immunohistochemistry to be present within duct lumina and in atrophied acini and their lumina. Alkaline phosphatase and Mg-ATPase specific activities were elevated in the hamster, but reduced in the rat, when compared with whole pancreas. Hamster alkaline phosphatase and Mg-ATPase were localized by histochemistry to the duct stroma, where these enzymes are not detected in vivo. Carbonic anhydrase was found in the duct epithelium of both species, as in vivo, as well as in the duct stroma, unlike in vivo. Acid glycosaminoglycans, as revealed by alcian blue staining, were found at the apical surfaces and in the lumina of both kinds of ducts. Glutathione-S-transferase and glucose-6-phosphate dehydrogenase were elevated in rat ducts, but not in hamster ducts. The polypeptide compositions of cultured ducts, freshly isolated pancreatic islets, and whole pancreas were compared by one-dimensional sodium dodecyl sulfate polyacrylamide gradient gel electrophoresis. No duct-specific polypeptides were observed; the ducts were characterized mainly by the reduction or absence of polypeptides, including some zymogens, seen in whole pancreas.