Role of endogenous interleukin-12 in immune response to staphylococcal enterotoxin B in mice

Abstract

In the present study, the roles of interleukin 12 (IL-12) and IL-18 and their possible interaction during superantigen-induced responses were studied by injection of staphylococcal enterotoxin B (SEB) into mice. These data suggest that the role of IL-12 in SEB-induced responses is limited to sustaining gamma interferon release by an IL-18-independent mechanism.

FIG. 1

Injection of SEB i.p. (100 μg) induces the expression of IL-12p35 and IL-12p40 mRNA in spleens and the systemic release of IL-12p70 and IL-12p40. (A) Spleens of three mice at each time point were pooled for IL-12 mRNA and β-actin mRNA expression as determined by RT-PCR. Molecular size markers are shown to the left. (B) Plasma concentrations of IL-12p70 and total IL-12p40 (mean ± standard error of the mean of results for six to eight mice per time point) were measured at the indicated time points after injection of SEB. Control mice received saline only.

FIG. 2

Concentrations of TNF, IL-2, IL-10, and IFN-γ in plasma of IL-12p40^−/− mice and WT mice after i.p. injection of 100 μg of SEB. Data are means ± standard errors of the means of results for six to eight mice at each time point. Asterisk, P value of <0.05 in comparison of results for IL-12p40^−/− mice and WT mice by the Mann-Whitney U test.

FIG. 3

Proliferation of Vβ8⁺ T cells among spleen (left panel) and mesenteric lymph node (right panel) cells in response to SEB in IL-12p40^−/− (closed symbols) and WT (open symbols) mice. Cell populations were determined by FACScan analysis. IL-12p40^−/− and WT mice were injected i.p. with NaCl (t = 0) or 100 μg of SEB and sacrificed at 2 or 4 days after injection. Values are means ± standard errors of the means of results for three mice per group. Data are expressed as percent positive cells within the lymphocyte population of spleen or mesenteric lymph node cells.

FIG. 4

Effect of anti-IL-18 on SEB-induced IFN-γ release in IL-12p40^−/− and WT mice. All mice were injected with 100 μg of SEB i.p. in combination with anti-IL-18 or control serum (200 μl) administered i.p. 1 h prior to SEB, and the mice were sacrificed after 8 h for IFN-γ measurements. Data are means ± standard errors of the means of results for six mice per group. Asterisk, P value of <0.05 in comparison of results for IL-12p40^−/− mice and WT mice by the Mann-Whitney U test.