Inhibition of tumor necrosis factor alpha alters resistance to Mycobacterium avium complex infection in mice.

Increased production of tumor necrosis factor alpha (TNF-alpha) appears to play an important role in the progression of human immunodeficiency virus disease. One treatment strategy being explored is the use of TNF-alpha inhibitors. TNF-alpha also appears to be important in conferring resistance to infections, and the inhibition of this cytokine may exacerbate the emergence of opportunistic pathogens, such as Mycobacterium avium complex (MAC). The present study examines the possibility that inhibition of TNF-alpha will increase the progression of disease in mice infected with MAC. C57BL/6 beige (bg/bg) mice have been shown to be highly susceptible to infection with MAC and are routinely used for testing of antimycobacterial drugs. However, bg/bg mice are known to exhibit impaired phagocyte and natural killer cell function. Since these cell types are important sources of TNF-alpha, the susceptibility of the bg/bg strain to infection with MAC was compared with those of the heterozygous (bg/+) and wild-type (+/+) strains of C57BL/6 mice. The susceptibilities of the bg/bg and bg/+ strains of mice infected with MAC were found to be comparable. The +/+ strain was the least susceptible. Mycobacterial burden and serum TNF-alpha levels increased over time in all the strains of mice tested. The bg/+ strain of C57BL/6 mice was then chosen to measure the activity of TNF-alpha antagonists. Treatment with dexamethasone decreased serum TNF-alpha levels and increased mycobacterial burden. Treatment with anti-TNF-alpha antibody or pentoxifylline did not significantly alter serum TNF-alpha levels but increased mycobacterial burden. Treatment with thalidomide neither consistently altered mycobacterial burden in the spleens or livers of infected mice nor affected serum TNF-alpha levels.

Monocyte culture and adherence modifies LPS-induced IL-6 production and inhibition by hydrocortisone.

The effect of hydrocortisone (HC) on IL-6 production by monocytes (Mo) that were cultured under either adherent or limited-adherent culture conditions was determined. Although freshly isolated Mo produced more IL-6 in response to LPS than Mo cultured 24 hr, culture had little effect on inhibition of IL-6 by HC. In contrast, the conditions of Mo culture had a significant impact on the kinetics of IL-6 production and inhibition by HC. Adherent Mo produced significantly higher levels of IL-6 4 hr after LPS compared to limited-adherent Mo. By 12 hr of LPS stimulation, comparable quantities of IL-6 were produced by both cultures. HC inhibition was complete 4 hr after LPS stimulation of adherent Mo, while 12 hr was required for maximum inhibition of limited-adherent Mo. Production of an IL-6 inhibitor was not responsible for the increased inhibition by HC with adherence, because both IL-6 protein and bioactivity were comparably decreased. The kinetics of inhibition of TNF alpha and IL-1 beta production by HC were similarly affected by adherence. Phenotypic analysis of cultured vs freshly isolated Mo showed a decrease in Mo expressing CD14, but not CD11b, which paralleled a decrease in IL-6 production by the cultured Mo. However, there were no phenotypic differences between adherent and limited-adherent Mo. The results demonstrate that the time of Mo culture, as well as adherence, may serve to alter LPS-induced IL-6 production and its inhibition by HC.

Hydrocortisone regulation of interleukin-6 protein production by a purified population of human peripheral blood monocytes.

The direct effect of the endogenous glucocorticoid (GC) hydrocortisone (HC) on interleukin-6 (IL-6) production was examined using purified populations of human peripheral blood monocytes (Mo). Lipopolysaccharide (LPS) induced IL-6 production by Mo in a dose-dependent fashion. IL-6 was detected in Mo supernatants as early as 2 hr after stimulation, with peak IL-6 production observed by 16 hr. Simultaneous addition of HC and LPS resulted in a significant decrease of IL-6 production 4 hr after LPS treatment, with maximum inhibition observed at 16-24 hr. An attenuation of the inhibitory effect of HC occurred with greater concentrations of LPS and with the delay of HC addition until after LPS. However, there was no correlation between the quantity of IL-6 produced by Mo and the level of HC inhibition. The inhibitory effect of HC was greater if LPS, rather than IL-1 beta, were used as a stimulus to induce IL-6 production. The EC50 of LPS-induced IL-6 production by HC was 2.0 x 10(-7) M. The inhibitory effect of HC on LPS-stimulated IL-6 production was GC specific and receptor mediated because: (i) equivalent inhibition was not observed with other endogenous steroids and (ii) equimolar amounts of the GC antagonist RU 486 blocked the GC-mediated effect.

Bone marrow derived macrophages have polyamine and ectoenzyme phenotypes distinct from resident macrophages.

Several prototype macrophage (MO) populations were compared for differences in ectoenzyme phenotype and polyamine content. Resident peritoneal MO and Corynebacterium parvum (CP)-activated peritoneal MO expressed unique ectoenzyme phenotypes, while bone marrow derived MO (BMDMO), obtained from stem cells after 7 days in culture with colony stimulating factor, and thioglycollate (TG)-elicited peritoneal MO exhibited a similar ectoenzyme phenotype. All of the MO populations, however, differed in polyamine accumulation patterns. These results suggest that ectoenzyme phenotypes do not serve as completely selective markers of MO differentiation. Moreover, BMDMO do not resemble steady state tissue peritoneal MO but appear to resemble inflammatory MO in several respects. Therefore activated BMDMO do not appear to provide an accurate model system for their continued use in studies to characterize the development of resident tissue MO.

Effect of inapparent murine hepatitis virus infections on macrophages and host resistance.

Inapparent infections of mice with murine hepatitis virus (MHV) altered host resistance to experimental infection with a second virus, encephalomyocarditis virus (EMC), reduced the protective effects of exogenously administered interferon against EMC infections, and it altered macrophage ectoenzyme phenotypes in two macrophage populations. Resident peritoneal macrophages from mice experimentally infected with one of two strains of MHV also demonstrated altered ectoenzyme phenotypes. These data demonstrate that inapparent infections with MHV alter several host resistance and macrophage parameters and directly demonstrate that effects of inapparent MHV infection on macrophage parameters can be reproduced experimentally.

Antimicrobial activity of various immunomodulators: independence from normal levels of circulating monocytes and natural killer cells.

The effects of 89Sr treatment on the natural host resistance of CD-1 mice and the enhancement of resistance by immunomodulators to infection with Listeria monocytogenes or herpes simplex virus type 2 (HSV-2) were determined. In the CD-1 mouse, single-dose treatment with 89Sr caused a profound decrease in the number of circulating monocytes (Mo), lymphocytes, and polymorphonuclear leukocytes (PMN) within 1 week. There was also marked functional impairment of the Mo inflammatory response, as well as markedly decreased spontaneous and activatable cytotoxicity by splenic natural killer (NK) cells. Despite this profound cellular suppression, there was no significant change in natural resistance of CD-1 mice to L. monocytogenes or HSV-2 infection. Furthermore, prophylactic treatment of mice with the biologic immunomodulator Corynebacterium parvum or the synthetic immunomodulators maleic anhydride-divinyl ether or avridine in liposomes resulted in comparable enhancement of resistance in 89Sr-treated and normal mice. These data indicate that natural and immunomodulator-enhanced resistance of CD-1 mice to microbial infections do not depend on normal levels of Mo, PMN, or NK cells. The resistance enhancement may rely on activated tissue macrophages (M phi). In contrast to the early changes in circulating leukocytes, the resident peritoneal cell populations were not markedly altered until after day 30. There then was a distinct decline in lymphocytes and a gradual decline in M phi; the change in M phi was apparently due to the lack of an age-related increase in the peritoneal M phi population in 89Sr-treated mice in comparison with a slight increase in resident M phi in normal mice. After CD-1 mice were treated with 89Sr, the number of PMN and the function of NK cells generally recovered by about day 50 and was followed by partial recovery of circulating Mo, unless a second dose of 89Sr was administered.

Selectively eliminated blood monocytes and splenic suppressor macrophages in mice depleted of bone marrow by strontium 89.

The contribution of specific activity to the effects of the bone-seeking isotope, strontium 89 on radiosensitive components of mononuclear phagocyte populations was investigated in mice. CBA/J mice received a fixed dose of 2 microCi/g body weight of 89Sr with three different specific activities, 6 Ci, 100 microCi and 20 microCi per mg Sr. The estimated radioactivity located in the bone surface was 4,200, 3,000 and 2,400 cpm/mg bone when measured 2 days after the administration of 89Sr, and was lost with an estimated biological half-life of 27, 25, and 23 days, respectively. Bone marrow suppression was assessed by quantitation of the depletion of macrophage-colony forming cells (M-CFC) grown in vitro in the presence of macrophage growth factor. The decline in M-CFC closely paralleled the level of radioactivity in the bone. These effects were clearly reflected by the depletion of monocytes in the blood, which were reduced to 14%, 14%, and 21% of control levels corresponding to SA's of 6 Ci/mg, 100 microCi/mg and 20 microCi/mg when counted on day 10. By day 30 the respective monocyte levels were 15%, 31%, and 77%. Furthermore, the induction of prostaglandin E producing suppressor macrophages (M phi) by Corynebacterium parvum administration was found to vary inversely with the effects of radioactivity in the bone, with initial impairment followed by quantitative recovery. Resident-type M phi in peritoneal cavity, however, appear to be unaffected by 89Sr-treatment. These data suggest, as before, that the monocytes and suppressor M phi are dependent on radiosensitive marrow cells. The observations also lead to the conclusion that the specific activity of 89Sr preparations is an important determinant of the degree of suppression and of the rate of recovery of bone marrow from the effects of irradiation that follow the administration of this isotope.

Lymphocyte function in experimental African trypanosomiasis. VI. Parasite-specific immunosuppression.

The ability of mice infected with African trypanosomes to produce antibodies to the surface antigen of the infecting trypanosome variant antigenic type upon primary and secondary exposure was examined. C57BL/10SnJ mice were infected initially with Trypanosoma rhodesiense clone LouTat 1.0. Surface antigen-specific antibody titers (IgM and IgG) to the infecting variant were measured throughout the course of infection; when the titers were sufficiently low, mice were reinfected with LouTat 1.0 trypanosomes and the antibody response was measured. Results demonstrate that mice in the early stage of infection exhibited transient suppression of antibody responses to LouTat 1.0 upon reexposure. In contrast, mice in the terminal phase of the disease were completely suppressed in their ability to mount a humoral response to LouTat 1.0. Trypanocidal chemotherapy of mice restored immunoresponsiveness in that treated mice responded with both IgM and IgG surface antigen-specific antibody to LouTat 1.0. The resulting antibody response, however, was more indicative of a primary humoral response to the parasites rather than a true secondary immune response.

Lymphocyte function in experimental African trypanosomiasis. V. Role of antibody and the mononuclear phagocyte system in variant-specific immunity.

The role of parasite-specific antibody and the mononuclear phagocyte system (MPS) in immunity to the African trypanosomes was examined. For this study C57BL/10SnJ mice were infected with Trypanosoma rhodesiense clone LouTat 1.0. Infected mice were injected with 75Se-labeled LouTat 1.0 trypanosomes, and clearance from the blood upon reexposure was measured throughout the course of infection. Clearance of labeled organisms occurred only on or after day 5, which was the day of natural elimination of LouTat 1.0 from the blood. Clearance was dependent on a functional immune system and correlated with the appearance of antibody to the variant-specific surface antigen (VSSA) of the trypanosomes. The ability to clear trypanosomes was transferred to normal, uninfected mice by immune serum. Both the IgM and IgG fractions of immune serum mediated the clearance, and VSSA-specific IgM fractions were as efficient in clearing LouTat 1.0 as the IgG fractions. Normal levels of complement (C3) were not required for clearance. The liver was the primary organ of clearance, and the ability of the liver to sequester radiolabeled trypanosomes was not impaired in the terminal phase of the disease or by large numbers of circulating trypanosomes present representing different variant antigenic types (VAT). We conclude that in African trypanosomiasis the MPS is not depressed in its ability to clear trypanosomes of the infecting VAT at any time during the course of infection. The observed clearance function requires parasite-specific antibody but normal levels of C3.