Modulation of Mycobacterium avium growth in vivo by cytokines: involvement of tumour necrosis factor in resistance to atypical mycobacteria

Gamma interferon-producing CD4+ T lymphocytes in the lung correlate with resistance to infection with Mycobacterium tuberculosis

The human immune system efficiently limits the replication of Mycobacterium tuberculosis in most infected individuals. Only 5 to 10% of infected people develop clinical tuberculosis, a sign of the inability of the immune system to control the infection. We have studied the C3H/HeJ (C3H) and C57BL/6 (B6) inbred mouse strains, which differ in their susceptibility to tuberculosis, in order to ascertain the immunological determinants of a successful immune response against M. tuberculosis and to establish a system to identify genes that influence susceptibility to tuberculosis. We found that the resistant B6 mice were able to control infection in both the lung and spleen, while susceptible C3H mice were incapable of limiting bacteria growth, especially in the lung, and succumbed to infection within 4 weeks. We determined that the susceptibility of C3H mice was independent of the Toll-like receptor 4 (tlr4) genetic locus and allelic major histocompatibility complex differences. Although the splenic immune responses were similar in the two mouse strains, the local immune responses in the lungs of the infected mice differed greatly. The pulmonary immune response in resistant B6 mice was characterized by an early influx of both CD4+ and CD8+ lymphocytes that produced gamma interferon (IFN-gamma). In contrast, the immune response of C3H mice in the lung was characterized by a delayed and decreased influx of lymphocytes, which produced little IFN-gamma. These results suggest an important role for the early appearance of IFN-gamma-producing lymphocytes in the lung in resistance to infection with M. tuberculosis.

Release of monocyte chemoattractant protein (MCP)-1 by a human alveolar epithelial cell line in response to mycobacterium avium

Clinical strains of Mycobacterium avium isolated from patients with acquired immunodeficiency syndrome, but not a non-clinical laboratory strain (ATCC 25291), were found to stimulate the human alveolar epithelial cell line A549, to produce monocyte chemoattractant protein (MCP)-1. A549 cells were also found to produce elevated levels of MCP-1 in response to sonicates of the clinical strains of M. avium, and surprisingly, the non-clinical strain as well. However, sonic extracts of the clinical strains were found to induce significantly higher levels of MCP-1 production compared to extracts of the non-clinical strain (P < 0.001). These data suggest the existence of strain-related differences in antigen expression by M. avium. The clinical and non-clinical strains of M. avium were found to attach and invade, but not replicate in A549 cells indicating that MCP-1 production by A549 cells does require the presence of viable, replicating organisms. Activation of alveolar epithelial cells by exposure to M. avium resulting in the production of chemokines which recruit inflammatory cells to the site of infection may be an important regulatory pathway for the activation of pulmonary host defense.

Minor role played by type I tumour necrosis factor receptor in the control of Mycobacterium avium proliferation in infected mice

Control of mycobacterial growth depends on the concerted activity of different cytokines acting in different stages of the development of innate and adaptive immune responses. Tumour necrosis factor-alpha (TNF-alpha) has been shown to play a protective role in Mycobacterium avium infections. Here we assessed the growth of this mycobacterial species in wild-type mice and in mice with a genetically engineered disruption of the type I receptor for TNF-alpha (p55-KO mice). p55-KO mice infected with a low-virulence strain of M. avium exhibited a slightly delayed capacity to eliminate the micro-organisms from the liver as compared with wild-type animals. However, either the growth of this strain in the other organs studied (spleen and lung) or the growth of two other strains of M. avium with intermediate or high virulence, failed to be affected by mutation of the TNF-alpha receptor. p55-KO mice were also as protected by the administration of recombinant interleukin-12 as the heterozygous p55 +/- mice. We conclude that signalling through the type I TNF receptor plays a small role in vivo in the induction of mycobacteriostasis during M. avium infection but may improve survival during infection with virulent mycobacteria, independently of the extent of their proliferation.

The modulating effects of proinflammatory cytokines interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), and immunoregulating cytokines IL-10 and transforming growth factor-beta (TGF-beta), on anti-microbial activity of murine peritoneal macrophages against Mycobacterium avium-intracellulare complex

We assessed the roles of proinflammatory cytokines IFN-gamma and TNF-alpha, and immunoregulatory cytokines IL-10 and TGF-beta in the modulation of the anti-microbial activity of murine peritoneal macrophages against Mycobacterium avium-intracellulare complex (MAIC). First, both IFN-gamma and TNF-alpha significantly reduced the bacterial growth in macrophages, indicating that these cytokines participate in up-regulation of macrophage anti-MAIC function. Second, although MAIC-infected macrophages produced substantial amounts of IL-10 and TGF-beta, neutralization of endogenous IL-10 and TGF-beta with anti-IL-10 and anti-TGF-beta antibodies, respectively, did not affect the intracellular growth of MAIC in macrophages from mice with BcgS (MAIC-susceptible) or BcgI (MAIC-resistant) genotype, regardless of the virulence of test MAIC strains. The same result was also obtained for macrophages stimulated with IFN-gamma or TNF-alpha. Third, in MAIC-infected mice, the growth of organisms at the sites of infection (lungs and spleens) was not affected by administration of anti-IL-10 or anti-TGF-beta antibodies. These findings indicate that, in the case of mice, endogenous IL-10 and TGF-beta are essentially ineffective in down-regulating macrophage anti-MAIC functions not only in vitro but also in vivo.

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.

Interleukin-12 in infectious diseases

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that is crucially involved in a wide range of infectious diseases. In several experimental models of bacterial, parasitic, viral, and fungal infection, endogenous IL-12 is required for early control of infection and for generation and perhaps maintenance of acquired protective immunity, directed by T helper type 1 (Th1) cells and mediated by phagocytes. Although the relative roles of IL-12 and gamma interferon in Th1-cell priming may be to a significant extent pathogen dependent, common to most infections is that IL-12 regulates the magnitude of the gamma interferon response at the initiation of infection, thus potentiating natural resistance, favoring Th1-cell development; and inhibiting Th2 responses. Treatment of animals with IL-12, either alone or as a vaccine adjuvant, has been shown to prevent disease by many of the same infectious agents, by stimulating innate resistance or promoting specific reactivity. Although IL-12 may enhance protective memory responses in vaccination or in combination with antimicrobial chemotherapy, it is yet unclear whether exogenous IL-12 can alter established responses in humans. Continued investigation into the possible application of IL-12 therapy to human infections is warranted by the role of the cytokine in inflammation, immunopathology, and autoimmunity.

Mycobacterium avium infection in mice is associated with time-related expression of Th1 and Th2 CD4+ T-lymphocyte response

Disseminated infection caused by organisms of Mycobacterium avium complex is common in acquired immune deficiency syndrome (AIDS) patients. M. avium is an intracellular bacterium that multiplies within macrophages. We examined the effect of M. avium infection on the T-helper cell response in C57/BL/6 black mice. At weekly intervals, CD4+ T-cells were isolated from spleens and lines were created. T-cell lines were exposed to sonicated M. avium in the presence of feeder cells and macrophages and the supernatant were collected to measure the concentrations of interferon-gamma (IFN-gamma and interleukin-10 (IL-10). Production of IFN-gamma in CD4+ T-cells obtained from uninfected mice did not vary significantly during the 5 weeks. Levels of IFN-gamma produced by T-cell lines of infected mice were similar to the control mice during the first 2 weeks but significantly reduced (approximately 30 ng/ml) thereafter. In contrast, production of IL-10 by T-cell lines of infected mice was in a range of 190 to 342 pg/ml in weeks 1, 2 and 3, but increased to an average of 1300 pg/ml at weeks 4 and 5. Pre-immunized mice, when infected with M. avium strain 101, showed a different profile of T-cell cytokines, with high IFN-gamma and low IL-10 production. Proteins purified from a number of disease-associated (D-A) and non-D-A strains of M. avium were tested for the ability to induce IL-10. 65,000 MW and 60,000 MW proteins of M. avium induced significantly more IL-10 than 45,000 MW, 33,000 MW and 27,000 MW proteins. These results showed that M. avium predominantly stimulates either Th1 or Th2 T-helper cells according to the phase of the infection.

Temporal effect of tumor necrosis factor alpha on murine macrophages infected with Mycobacterium avium

Members of the Mycobacterium avium complex are a family of bacteria that persist within macrophages in the face of an immune response. Elimination of these organisms is likely due to cytokine-induced macrophage activation. Because macrophage activation by tumor necrosis factor alpha (TNF-alpha) appears critical for killing of intracellular M. avium, early downregulation of TNF-alpha levels in infected macrophages has been suggested as a survival mechanism for virulent strains of M. avium. We examined the relationship between TNF-alpha and growth of M. avium strains of differing virulence, as measured by their ability to grow in murine bone marrow-derived macrophages. When exogenous TNF-alpha was added immediately following macrophage infection, significant growth inhibition of virulent M. avium strains was observed. If TNF-alpha addition was delayed by 24 h or more, growth inhibition was abrogated. To determine if early downregulation of TNF-alpha levels could explain the differential growth of virulent and avirulent strains, levels of TNF-alpha and prostaglandin E2 (PGE2), which has been shown to suppress TNF-alpha production in uninfected macrophages, were quantified over time. Upregulation of both TNF-alpha and PGE2, as measured by enzyme-linked immunosorbent assay, was evident by 6 h postinfection, indicating that the ability of M. avium to replicate in macrophages was not directly correlated with early downregulation of TNF-alpha production. However, TNF-alpha bioactivity, as measured by cytotoxicity, was significantly decreased in virulent M. avium strains at all time periods examined. Treatment of infected macrophages with gamma interferon immediately after infection resulted in significantly increased levels of nitric oxide but did not affect the growth of virulent M. avium strains. These results suggest that while significant levels of TNF-alpha are present in supernatants from all M. avium strains, levels of biologically active TNF-alpha are significantly reduced in supernatants from virulent M. avium strains. Preliminary results suggest that upregulation of the soluble p75 TNF receptor may be one mechanism by which TNF-alpha bioactivity reduction occurs.

Bidirectional effects of IFN-gamma on growth of Mycobacterium avium complex in murine peritoneal macrophages

The effects of macrophage stimulation with interferon-gamma (IFN-gamma) before or after infection on the intracellular growth of Mycobacterium avium complex (MAC) were investigated. Treatment of murine peritoneal macrophages before infection with IFN-gamma (50 U/ml) for 24 h and 48 h, but not for 72 h, was associated with 41% and 52% significant MAC growth inhibition, respectively. NG-monomethyl-L-arginine (NMA) did not affect the preinfection antimycobacterial activity of IFN-gamma, thus indicating that nitric oxide was not involved in this phenomenon. In contrast, treatment of macrophages with IFN-gamma (50 U/ml) for 24 h and 48 h after infection was ineffective, whereas treatment for 72 h caused some MAC growth promotion. The use of NMA suppressed the IFN-gamma-mediated MAC growth, suggesting that nitric oxide may affect postinfection microbicidal function of macrophages. These results suggest that activation of macrophages with IFN-gamma before or after infection may direct the course of the infection and that nitric oxide may be detrimental more than beneficial for MAC-infected macrophages.

Evidence for a reduced chemokine response in the lungs of beige mice infected with Mycobacterium avium

The basis of the increased susceptibility of beige mice to Mycobacterium avium infections is still not clearly understood. In this study we examined the growth of three virulent strains of M. avium in beige mice and normal C57BL/6 controls. Depletion of natural killer (NK) cells by administration of anti-asialo GM1 antisera did not affect the growth of M. avium in any of the groups of animals. Similarly, interferon-gamma (IFN-gamma) gene-disrupted mice were more susceptible to infection than control mice but the growth of M. avium was not further affected by NK-cell depletion. In terms of effector immunity, beige mice showed enhanced expression of IFN-gamma and tumour necrosis factor-alpha (TNF-alpha) when compared with wild-type C57BL/6 mice. In agreement with these results; I-A and interferon-inducible protein (IP-10) expression was also higher in beige mice than in wild-type animals, as was expression of the chemokines macrophage inflammatory protein-2 (MIP-2) and macrophage chemotactic protein (MCP-1) during latter stages of the infection. However, over the first few weeks of the infection, when the susceptibility of the beige mouse lung first becomes evident, MIP-1 beta and MIP-2 chemokine expression in the lungs was lower in beige mice than in wild-type animals. These data indicate, therefore, that the increased susceptibility of beige mice to M. avium infection in the lung is not due to lack of NK-cell activity, nor can it be explained in terms of the effector cytokine response. Instead, the lower early expression of the neutrophil chemoattractants MIP-1 beta and MIP-2 in the lungs of beige mice tends to suggest that the enhanced susceptibility of these mice to M. avium infection may be due in part to defective recruitment of neutrophils or other cells responsive to these specific chemokines.

Effects of benzoxazinorifamycin KRM-1648 on cytokine production at sites of Mycobacterium avium complex infection induced in mice

Although various antimicrobial agents exhibit appreciable microbicidal activity in the early phase (weeks 2 t0 4) of Mycobacterium avium complex (MAC) infection induced in mice, progressive bacterial regrowth subsequently occurs. To clarify the reason for this pattern of changes, we studied changes in the levels of various cytokines in tissue at sites of infection (spleens and lungs) of MAC-infected mice which were or were not given a benzoxazinorifamycin, KRM-1648 (KRM). Levels of the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) in tissues temporarily increased at around weeks 2 to 4 after infection, rapidly decreased thereafter, and returned to normal by week 8. Similar but somewhat delayed changes were noted for levels of interleukin 10 (IL-10) and transforming growth factor beta (TGF-beta), immunosuppressive cytokines with macrophage (M phi)-deactivating activity, in tissue, except that TGF-beta levels in the spleen remained high during weeks 4 to 8. KRM treatment blocked the increase in the levels of all of those cytokines in tissue in the early phase of infection, most strongly at week 4. IL-6 levels were beneath the limit of detection throughout the observation period. Bacterial loads in the visceral organs decreased during the first 2 weeks, and KRM treatment markedly promoted this decrease. However, regrowth of MAC organisms began at weeks 2 to 4 and continued thereafter, even in KRM-treated mice. Splenocytes and splenic M phi s of MAC-infected mice (week 2) produced and/or released into the culture fluid significant amounts of TNF-alpha (in a cell-bound form), IFN-gamma, and IL-10, but not TGF-beta, during 3 days of cultivation. A substantial amount of TGF-beta was produced during 2 weeks of cultivation of peritoneal M phi s. KRM itself did not significantly affect the IL-10- and TGF-beta-producing ability of cultured M phi s. These findings suggest that IL-10 and TGF-beta play important roles in the regrowth of MAC organisms seen during the course of KRM treatment.

Macrophage release of tumor necrosis factor-alpha by Mycobacterium avium antigens

Mycobacterium avium complex (MAC) infection is the most common disseminated opportunistic infection encountered in patients with AIDS. We have studied the ability of specific Mycobacterium avium (MA) antigen to stimulate human monocyte-derived macrophages (MDM) to produce tumor necrosis factor-alpha (TNF-alpha). MDM stimulated with MA sonicate, MA 68 kDa and MA 48-52 kDa antigens were found to produce TNF-alpha in a dose-dependent manner. Reverse transcriptase-polymerase chain reaction analysis of mRNA extracts from antigen-stimulated MDM indicated that TNF-alpha mRNA expression was of brief duration and the time point of peak TNF-alpha mRNA levels was found to be antigen-specific. A significant difference in TNF-alpha production in response to MA 48-52 kDa antigen and M. bovis 65 kDa antigen was observed between MDM from normal and HIV positive individuals.

Cytokine secretion and adhesion molecule expression by granuloma T lymphocytes in Mycobacterium avium infection

Mice experimentally infected with Mycobacterium avium develop a chronic disease characterized by widespread noncaseating granulomas. In this report, we describe the phenotype and cytokine secretion profile of these granuloma-infiltrating effector T lymphocytes. In response to specific antigen, granuloma T cells and, to a lesser extent, spleen cells secrete interferon-gamma, but no interleukin-4 or -5. The importance of this Th1-like response to the host was demonstrated by the massively increased bacterial load and lethal disease in interferon-gamma knockout mice. One function of localized cytokine secretion is to recruit inflammatory T cells bearing surface adhesion molecules complementary to counter-receptors on vascular endothelial cells. Granuloma T cells express high levels of these pro-inflammatory adhesion molecules but have down-regulated their expression of L-selectin (CD62L). The expression of these adhesion molecules on granuloma-infiltrating T lymphocytes would alter the migration pathway of these cells and is likely to be important in facilitating the traffic of effector T cells to the granulomatous inflammatory site. In addition, T cells from Schistosoma mansoni granulomas express the same set of adhesion molecules, showing that this phenotype is not specifically dependent upon the Th1 pattern of cytokine secretion.

Increased intestinal TNF-alpha, IL-1 beta and IL-6 expression in ovine paratuberculosis

Mycobacterium avium subspecies paratuberculosis is an intracellular parasite of intestinal macrophages and causes a chronic granulomatous enteritis in sheep and other ruminants (paratuberculosis or Johne's disease). Macrophages can be produced a variety of immunoregulatory cytokines that may influence mycobacterial killing and produce disordered inflammation within the gut. In this study, messenger RNA (mRNA) was extracted from intestinal tissue from control and multibacillary diseased sheep and profiles for the cytokines tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), IL-6, transforming growth factor-beta1 (TGF-beta1) and granulocyte-macrophage colony stimulating factor (GM-CSF) were semi-quantified using reverse transcriptase polymerase chain reactions (RT-PCR). Infected intestinal tissues had significantly increased mRNA for TNF-alpha, IL-1beta and IL-6 but TGF-beta1 and GM-CSF mRNA levels were significantly different from controls. Supernatants from in vitro intestinal cultures were assayed for TNF-alpha activity using the PK(15)-1512 cytotoxicity bioassay and levels were significantly raised in diseased samples. TNF-alpha was not detected in any serum samples. Further analysis on intestinal tissues from sheep with the different, paucibacillary, form of the disease showed significant elevation of TNF-alpha mRNA but not other cytokines tested. Increased pro-inflammatory cytokine expression in the intestine coincident with a failed or misdirected immune response may contribute to the pathogenesis of paratuberculosis and the persistence of a chronic inflammatory state.

Relationship between virulence of Mycobacterium avium strains and induction of tumor necrosis factor alpha production in infected mice and in in vitro-cultured mouse macrophages

We studied the ability of two Mycobacterium avium strains with different virulences to induce tumor necrosis factor alpha (TNF) synthesis by mouse resident peritoneal macrophages (RPM phi) in vitro in an experiment to look for a possible correlation between virulence and this TNF-inducing capacity. The low-virulence strain, 1983, induced significantly higher production of TNF by RPM phi than did the high-virulence strain, ATCC 25291. TNF neutralization during culture of infected RPM phi resulted in enhancement of growth of strain 1983 and had no effect on growth of strain ATCC 25291; TNF treatment of strain ATCC 25291-infected macrophages had no effect on mycobacterial growth. The extent of M. avium growth and the amount of TNF synthesis were independent of the presence of contaminating T cells or NK cells in the macrophage monolayers. Intraperitoneal administration of anti-TNF monoclonal antibodies to BALB/c mice infected intravenously with M. avium 1983 abrogated the elimination of the bacteria in the liver and caused a slight increase in bacterial growth in the spleen. Neutralization of TNF led to a minor increase in the proliferation of M. avium ATCC 25291 in the liver and spleen of BALB/c mice late in infection. Anti-TNF treatment did not affect the growth of the two M. avium strains in BALB/c.Bcgr (C.D2) mice, suggesting that restriction of M. avium strains to induce TNF production by macrophages may limit their ability to proliferate both in vitro and in vivo.

Protection of mice from Mycobacterium avium infection by recombinant interleukin-12

Treatment with interleukin-12 (IL-12) significantly reduced the number of viable bacteria in mice infected with Mycobacterium avium. IL-12 itself, however, could not inhibit directly mycobacterial growth in vitro. IL-12 exerts antimycobacterial activity in vivo with a low level of toxicity, possibly by enhancing the host defense against the infection.

Role of gamma interferon and tumor necrosis factor alpha during T-cell-independent and -dependent phases of Mycobacterium avium infection

To design an effective immunotherapy for Mycobacterium avium infections, the protective host response to the infection must be known. Here we analyzed the role of gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) in the innate and acquired responses to M. avium infections in mice. T-cell depletion studies showed that CD4+ T cells were required for control of the infection. CD(4+)-depleted mice showed enhanced bacterial proliferation and at the same time showed a reduction in the level of expression of both IFN-gamma and TNF-alpha mRNAs in spleen cells. In contrast, M. bovis BCG immunization restricted M. avium proliferation and at the same time promoted expression of the mRNAs for the two cytokines. In vivo depletion studies using specific monoclonal antibodies showed that both IFN-gamma and TNF-alpha are involved in an early protection possibly involving NK cells, and furthermore, IFN-gamma is involved in the later T-cell-protective response to infection. In vivo neutralization of IFN-gamma during M. avium infection also blocked the priming for enhanced TNF-alpha secretion triggered by endotoxin. Both cytokines were found to be involved in the resistance expressed in BCG-immunized animals and exhibited additive bacteriostatic effects in vitro on bone marrow-derived macrophages infected with different strains of M. avium. These data suggest that both cytokines act in an additive or synergistic fashion in the induction of bacteriostasis and that IFN-gamma is also involved in priming TNF-alpha secretion.

Effector mechanisms involved in cytokine-mediated bacteriostasis of Mycobacterium avium infections in murine macrophages

In this study we found that addition of a range of doses of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), or granulocyte-macrophage colony stimulating factor (GM-CSF) to cultures of bone marrow-derived murine macrophages infected with the 25291 strain of Mycobacterium avium gave rise to varying degrees of bacteriostasis. In contrast, similar treatment with interleukin-4 (IL-4) or IL-6 had no effect. However, when similar experiments with the former set of cytokines were performed using a panel of M. avium isolates, substantial isolate-to-isolate variation was observed. In cultures containing IFN-gamma, synthesis of substantial levels of reactive nitrogen intermediates was observed; however, neither these materials, nor reactive oxygen intermediates, were found to be responsible for observed bacteriostasis. In further experiments, in which the culture medium was supplemented with various concentrations of a weak acid or a weak base in order to influence the pH of macrophage intracellular compartments, it was found that the presence of the weak acid augmented the activity of IFN-gamma, whilst the weak base counteracted this effect. These data support the hypothesis, therefore, that the bacteriostatic effect of IFN-gamma against the growth of M. avium, rather than depending on reactive radical production, is mediated through acidification of the infected phagosome, perhaps through activation of proton pumps in the phagosomal membrane.

Differential expression of tumor necrosis factor and interleukin-6 by peritoneal macrophages in vivo and in culture

To investigate the differences in cytokine regulation in vitro as compared to in vivo, we examined the synthesis of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) by peritoneal macrophages in response to lipopolysaccharide (LPS). Mice (CBA/J) were primed with an intraperitoneal injection of complete Freund's adjuvant and after 2 weeks, peritoneal cells were harvested for culture or mice were injected intraperitoneally with LPS for in vivo studies. In ascites fluid, TNF-alpha peaked 1 hour after LPS and returned to baseline levels by 4 hours. In contrast, TNF-alpha in the media reached maximum at 7 hours. Expression of TNF-alpha messenger (m)RNA in vivo was rapid but transient, as levels peaked at 15 minutes and returned to baseline 1 hour after LPS. In contrast, TNF-alpha mRNA in vitro became maximal at 1 hour, but remained elevated to 5 hours after LPS. In vivo, IL-6 in ascites fluid peaked at 2 hours, whereas in vitro, IL-6 continued increasing to 24 hours. In vivo, IL-6 mRNA reached maximum at 30 minutes, but fell below baseline by 1.5 hours after LPS. In contrast, IL-6 mRNA in vitro was sustained at maximal expression between 5 to 9 hours after LPS. These results demonstrate that both TNF-alpha and IL-6 synthesis is more rapid in vivo than in vitro. The rapid kinetics of cytokine expression in vivo must considered when designing strategies to inhibit cytokine action in vivo.

Inhibition of growth of Mycobacterium avium in murine and human mononuclear phagocytes by migration inhibitory factor

Infections caused by Mycobacterium avium, the most common form of diseminated bacterial disease in AIDS patients, are difficult to treat because of their resistance to many antimycobacterial drugs. The results of the present study show that recombinant migration inhibitory factor, a 12-kDa molecule recently isolated by COS-1 cell expression screening of cDNA from a human T-cell hybridoma, has potent inhibitory activity on the growth of a panel of clinical isolates of M. avium within both bone-marrow-derived murine macrophages and cultured human blood monocytes. These cells cultured in recombinant migration inhibitory factor exhibit various signs of activation, including cell division, morphological changes such as evidence of substantial phagolysosomal fusion, and enhanced secretion of tumor necrosis factor.

Interferon-gamma and resistance to bacterial infections

Since its initial description as an antiviral, it has become clear that Interferon-gamma (IFN-gamma) has potent immunoregulatory and cell growth regulatory activities. As a result of these additional activities, it is now apparent that IFN-gamma plays a major role in regulation of bacterial infections. IFN-gamma can be both induced by bacteria and bacterial products; endogenous IFN-gamma production has been shown to play a protective role in the natural host response to several bacterial infections; and administration of exogenous IFN-gamma is effective in the prevention and treatment of bacterial infections in numerous animal model systems. Although it is now clear that IFN-gamma plays a role in regulation of bacterial infections, the mechanisms of its anti-bacterial effects in vivo remain to be established due to the pleiotropic nature of IFN-gamma activity.

Effect of blocking TNF-alpha on intracellular BCG (Bacillus Calmette Guerin) growth in human monocyte-derived macrophages

Four agents, thalidomide, oxpentifylline, dexamethasone and a polyclonal anti-TNF-alpha antibody, were all shown by specific Elisa to block endogenous TNF-alpha production by Bacillus Calmette Guerin (BCG)-infected human monocyte-derived macrophages in in vitro culture. There was however no significant enhancement of intracellular BCG growth, over a 7-day incubation, in human monocyte-derived macrophages in the presence of any of the TNF-alpha-blocking agents, as determined by both radiometric and CFU counting methods of assessing bacterial viability and growth. The result suggests that the action of TNF-alpha alone is unlikely to be an important effector mechanism in antimycobacterial immunity within human cells.

Capacity of Mycobacterium avium isolates to grow well or poorly in murine macrophages resides in their ability to induce secretion of tumor necrosis factor

The results of this study show that clinical isolates of Mycobacterium avium fall into two categories in terms of their capacity to grow within murine bone marrow-derived macrophage cultures: those that grow progressively and those that are incapable of growing within such cells. Members of the first category were invariably of the smooth-transparent colonial type, while most of the second were of the smooth-doomed type. In addition, this paper shows that although all isolates induced tumor necrosis factor (TNF) secretion by host cells to some extent, this production was always delayed in isolates that subsequently grew well in the host cells. This observation, coupled with the demonstration that the growth of the latter isolates was inhibited by the exogenous addition of TNF, leads us to hypothesize that the ability of a given isolate to somehow avoid host macrophage TNF production early during the course of the infection is a key factor in the pathogenesis of the disease.

Tumor necrosis factor plays an essential role in determining hypersensitivity pneumonitis in a mouse model

We examined the importance of the cytokine tumor necrosis factor-alpha (TNF-alpha) in a mouse model of hypersensitivity pneumonitis (HP). Mice of the C57BL/6 strain were instilled intranasally 3 days/wk for 3 wk with 150 micrograms of the actinomycete Faenia rectivirgula (Micropolyspora faeni) to induce HP as a model of farmer's lung. This experimental model was associated with a progressive inflammation in the lungs of challenged mice, seen histologically as cellular infiltrates of large quantities of macrophages and lymphocytes and some neutrophils. The disease in challenged mice treated with a control rabbit serum was also associated with a substantial release of tumor TNF-alpha (up to 80 U/ml of TNF-alpha in the bronchoalveolar lavage [BAL] at 3 wk after beginning of treatment) and interleukin-1, which peaked at 1 wk (approximately 300 U/ml) and diminished thereafter. A very large increase in BAL cell number (11-fold increase versus saline controls) and an enhanced release potential for TNF-alpha by alveolar macrophages was also seen. Lung fibrosis was also evident in challenged animals, as demonstrated by a 2-fold increase in hydroxyproline levels. Infusion of challenged mice with a rabbit polyclonal antibody against TNF-alpha (2 mg/wk) completely abrogated the disease, as mice so treated had normal lung histology. Anti-TNF-alpha blocked cellular recruitment in the lungs (only a 2-fold increase at week 3); it also completely abolished TNF-alpha secretion in the BAL and drastically reduced interleukin-1 levels in this fluid. Anti-TNF-alpha also abolished lung index increases and lung fibrosis, with both parameters similar to that of saline-instilled mice.(ABSTRACT TRUNCATED AT 250 WORDS)