Poly I:C or IFN-alpha/beta treatment inhibits macrophage induced T cell proliferation

Attrition of bystander CD8 T cells during virus-induced T-cell and interferon responses

Experiments designed to distinguish virus-specific from non-virus-specific T cells showed that bystander T cells underwent apoptosis and substantial attrition in the wake of a strong T-cell response. Memory CD8 T cells (CD8(+) CD44(hi)) were most affected. During acute viral infection, transgenic T cells that were clearly defined as non-virus specific decreased in number and showed an increase in apoptosis. Also, use of lymphocytic choriomeningitis virus (LCMV) carrier mice, which lack LCMV-specific T cells, showed a significant decline in non-virus-specific memory CD8 T cells that correlated to an increase in apoptosis in response to the proliferation of adoptively transferred virus-specific T cells. Attrition of T cells early during infection correlated with the alpha/beta interferon (IFN-alpha/beta) peak, and the IFN inducer poly(I:C) caused apoptosis and attrition of CD8(+) CD44(hi) T cells in normal mice but not in IFN-alpha/beta receptor-deficient mice. Apoptotic attrition of bystander T cells may make room for the antigen-specific expansion of T cells during infection and may, in part, account for the loss of T-cell memory that occurs when the host undergoes subsequent infections.

Nitric oxide mediates immunosuppression induced by Listeria monocytogenes infection: quantitative studies

Our laboratory has shown that immunization of mice with an attenuated strain of Salmonella typhimuriuminduces profound suppression in the capacity of splenocytes to mount an in vitro antibody plaque-forming cell (PFC) response to sheep red blood cells (SRBC) and to proliferate in response to mitogens. In vitro addition of NG-monomethyl-L-arginine (NMMA), an inhibitor of nitric oxide (NO) synthase, to cell cultures from Salmonella-immunized mice completely blocked suppression of the PFC responses, implicating that NO is the suppressor factor. The present study quantified the role of nitric oxide in immunosuppression induced by Listeria monocytogenes, a gram positive intracellular pathogen of macrophages. Listeria infection resulted in suppression of the PFC assay at inoculating doses of greater than 6.5x10(3)colony forming units, with no suppression observed at lower doses. Suppression correlated with increased nitrite production. Addition of NMMA to spleen cell cultures taken from Listeria-infected mice completely blocked suppression of the PFC response, and returned nitrite production to baseline levels. In regard to Listeria-induced suppression of responses to the mitogen, Concanavalin A (Con A), the parameters were different from those observed for the PFC response. There was a direct correlation between the log10of the inoculating dose of Listeria and degree of immunosuppression, with suppression observed at doses as low as 1x10(3)cells. Addition of NMMA to the Con A-stimulated cultures resulted in reduced nitrite levels, but only partial restoration of the proliferative responses. Co-culture of splenocytes from Listeria inoculated mice with normal splenocytes in media with NMMA and reduced levels of L-arginine resulted in complete reversal of suppressed responses to Con A. Similar differences in ease of reversing suppression of the PFC response, as compared with responses to Con A, were previously noted using cells taken from Salmonella-infected mice. The present results show that a gram positive intracellular pathogen of macrophages, L. monocytogenes, induces immunosuppression in mouse spleen cells by a nitric oxide mediated mechanism that closely parallels that induced by the gram negative pathogen, S. typhimurium.

Effect of exogenous cytokines on the inhibition of macrophage-induced, antigen-specific T cell proliferation by poly(I:C)

We have previously demonstrated that IFN-alpha/beta, poly(I:C) (an inducer of IFN-alpha/beta), or IFN-gamma can inhibit the ability of KLH-pulsed peritoneal macrophages (M phi) to induce the proliferation of syngeneic, KLH-immune T lymphocytes from CBA/J mice. In this study we investigated whether the mechanism by which poly(I:C) inhibits M phi-induced, antigen-specific T cell proliferation involved decreased cytokine production by poly(I:C) treated KLH-pulsed M phi or by T cells cultured with these M phi. The production of IL-2 by T cells cultured with poly(I:C)-treated, KLH-pulsed M phi was decreased by 80%; however, addition of exogenous rIL-2 could not restore proliferation. Although IL-1 production by poly(I:C)-treated M phi was comparable to the level produced by saline-treated, KLH-pulsed M phi controls, addition of exogenous rIL-1 was still examined to explore the possibility that a greater amount of IL-1 may be needed to induce T cell proliferation with poly(I:C)-treated, KLH-pulsed M phi. Increasing concentrations of rIL-1 alone or with rIL-6 did not abrogate the inhibition of M phi-induced, antigen-specific T cell proliferation by poly(I:C). Interestingly, the addition of combinations of IL-1 and IL-6 increased the proliferation of T cells in response to KLH presented by either saline- or poly(I:C)-treated M phi. The effect of the combination of rIL-1 and rIL-6 was synergistic in that addition of either monokine alone had no effect on T cell proliferation. These results suggest that although poly(I:C)-induced inhibition of T cell proliferation is not due to insufficient quantities of IL-1, IL-2, or IL-6, a combination of IL-1 and IL-6 can augment proliferation of freshly isolated T cells in response to antigen presented by freshly isolated accessory cells.

Splenic and inguinal lymph node T cells of aged mice respond differently to polyclonal and antigen-specific stimuli

Numerous changes have been reported to occur in T cell responsiveness of mice with increasing age. However, most of these studies have examined polyclonal stimulation of spleen cells from a limited number of mouse strains. This study investigated the influence of genetic background, source of lymphocytes, and type of stimulus on age-associated changes in T cells response. Con A-induced proliferation and IL-2 and IFN-gamma production by splenic lymphocytes (SL) was significantly greater in CBA/Ca mice compared to C57BL/6 mice, regardless of age. SL of both strains exhibited the predicted age-dependent decline in proliferative response and an increase in IFN-gamma production in response to Con A. In contrast, however, only SL from C57BL/6 mice demonstrated the predicted age-dependent decline in Con A-induced IL-2 production; Con A-induced SL of young and aged CBA/Ca mice produced comparable amounts of IL-2. Differences in age-associated responses to Con A were also observed between SL and inguinal lymph node (ILN) cells of CBA/Ca mice. In contrast to SL, ILN cells demonstrated an increased proliferative response to Con A. However, lymphokine production by Con A-stimulated ILN cells from aged CBA/Ca mice was similar to that of Con A-stimulated SL from aged CBA/Ca mice. To determine if aged ILN T cells respond similarly to polyclonal and antigen-specific stimuli, keyhole limpet hemocyanin (KLH) responses of T cells isolated from ILN of aged and young CBA/Ca mice were examined. KLH-specific T cells from aged mice cultured with KLH-pulsed macrophages (M phi) from aged mice were significantly reduced in their ability to proliferate compared to KLH-specific T cells of young mice cultured with young KLH-pulsed M phi. In contrast to the expected results, the defect was not at the level of the T cells; proliferation of young T cells cultured with aged KLH-pulsed M phi was equivalent to the proliferation of aged T cells cultured with aged M phi. These results suggest that aging has differential effects on polyclonal and antigen-specific T cell proliferation and on polyclonal stimulation of T cells isolated from different lymphoid organs and from different strains of mice.

Altered macrophage antigen-presenting cell function following Friend leukemia virus infection

To investigate the mechanism by which Friend leukemia virus (FV) causes immunosuppression, the ability of peritoneal macrophages to mediate antigen-specific T-cell activation following FV infection was examined. Decreased IL-2 production was observed when antigen-primed T cells were cultured with antigen-pulsed macrophages from mice infected with FV, compared to T cells cultured with macrophages from control mice. Macrophages from FV-infected mice demonstrated decreased phagocytic and pinocytic activity, suggesting that antigen uptake may be impaired in these cells. In addition, FV-infected mice had decreased numbers of MHC class II positive macrophages compared to uninfected controls, as measured by immunofluorescence. The alterations in antigen uptake and class II expression observed in macrophages from FV-infected mice may be the result of infection of these cells by FV, which was demonstrated by in situ hybridization using a FV-specific probe. The ability of FV to infect and modulate the functions of macrophages may account, at least in part, for the immunosuppression observed in FV-infected mice.

Inhibition of macrophage-induced antigen-specific T lymphocyte proliferation by poly I:C: strain and antigen independence

We have previously demonstrated that IFN-alpha/beta, poly I:C (an inducer of IFN-alpha/beta), and IFN-gamma can inhibit the ability of KLH-pulsed peritoneal macrophages to induce proliferation of syngeneic, KLH immune T lymphocytes in CBA/J mice. In this study, we show that this IFN-induced immunosuppression is not restricted to CBA/J (H-2k) mice but is also seen in BALB/cJ (H-2d) mice. A similar inhibition of proliferation is observed with the KLH-specific T cell hybridoma BDK, 100, which requires KLH-pulsed macrophages for optimum proliferation and IL-2 production. The immunosuppression produced by IFN was also independent of the antigen employed. Inhibition of T lymphocyte proliferation was observed when casein, instead of KLH, was used to immunize T cells and to pulse peritoneal macrophages in vivo. Utilizing KLH and casein, the antigen specificity of the inhibition was demonstrated. Therefore, the inhibition by the IFN-inducer poly I:C of macrophage-induced, antigen-specific T cell proliferation is not limited by H-2 type of the mice or to one antigen.

Varying role of alpha/beta interferon in the antiviral efficacy of synthetic immunomodulators against Semliki Forest virus infection

The question of whether interferon alpha/beta is the common mechanism of antiviral action of synthetic immunomodulators was investigated in B6C3F1 mice infected with Semliki Forest virus. Mice were treated with various concentrations of normal sheep serum or potent anti-alpha/beta interferon antiserum, inoculated with the immunomodulators, and infected 24 hours later with virus. Three patterns emerged. The antiviral action of the pyrimidinone (ABMP) and the oral interferon inducer (CL246,738) appeared to be mediated primarily by interferon alpha/beta; their protective ability was almost completely abrogated by treatment with low levels of anti-alpha/beta interferon antiserum. The antiviral action of two other immunomodulators, a mismatched polyribonucleotide (Ampligen) and a polyanionic copolymer (MVE-2) at least partially involved interferon. Activity of these compounds was reduced, but not consistently eliminated by treatments with high doses of antiserum. The antiviral activity of another polyribonucleotide, polyriboinosinic-cytidylic acid complexed with lysine carboxymethylcellulose (poly ICLC), was not affected by treatment with even the highest amount of antiserum (two injections of 100,000 neutralizing units each). Almost complete protection by poly ICLC was observed despite the fact that this high concentration of antiserum, when given alone, caused a decrease in natural resistance to Semliki Forest virus infection. Taken together, these results indicate that induction of interferon alpha/beta does not appear to be the major common mechanism of antiviral activity among these diverse synthetic immunomodulators.

Inhibition of macrophage-induced antigen-specific T-cell proliferation by interferon-gamma

The effects of IFN-gamma on macrophage (M phi)-mediated antigen-specific T-cell proliferation was investigated. A well-defined assay system using purified resident populations of antigen-pulsed peritoneal M phi and immune T cells was used to measure M phi-induced antigen-specific T-cell proliferation. Antibody affinity purified or recombinant IFN-gamma inhibited M phi-induced T-cell proliferation when KLH-pulsed M phi from mice given IFN-gamma prior to KLH were cultured with KLH immune T cells from normal mice. Monoclonal rat anti-IFN-gamma antibody neutralized the inhibitory effect of IFN-gamma. This inhibition of T-cell proliferation occurred despite the fact that these M phi appeared to be activated by IFN-gamma treatment as measured by increased tumoricidal activity. The mechanism for the inhibition was unrelated to class II (Ia) expression, IL-1 secretion, and prostaglandin secretion. These results demonstrate the complex and sensitive role IFN-gamma has in regulating the immune response.