This study was conducted to identify and quantify, over time, selected cytokine responses in Long–Evans rats that were exposed to staphylococcus enterotoxin B (SEB). The kinetics of selected cytokines [interleukin-2 (IL-2), IL-6, interferon-γ (IFN-γ) and tumour necrosis factor (TNF)] and phenotype and cell cycle analysis of T lymphocytes were determined in Long–Evans rats administered a single intraperitoneal (i.p.) dose of either 50 μg or 500 μg of SEB. Rats injected with 50 μg SEB had significantly elevated levels of IL-2, IL-6 and IFN-γ in their serum 2 hr post-injection. IL-2 serum levels were significantly elevated at 2 hr and returned to near control values by 12 hr while both IL-6 and IFN-γ peaked at 6 hr but remained significantly increased at 24 hr post SEB exposure. A 500 μg dose of SEB did not further enhance these cytokine responses. When spleen cells were collected for culture 2 hr after rats were injected i.p. with 50 μg SEB and cocultured with SEB, TNF and IL-6 levels were significantly increased after 2 hr incubation, while IL-2 and IL-6 were significantly elevated at 6 hr. Production of all these cytokines in spleen cell cultures continued to increase over the 24 hr sampled. Peritoneal cells were collected for culture either at 1 hr or 2 hr after injection of either 50 μg or 500 μg of SEB. IL-6 was significantly increased after 1 hr in culture while TNF was significantly increased by 2 hr regardless of whether the cells were harvested 1 or 2 hr after SEB injection. The greatest response for both IL-6 and TNF occurred when cells from animals injected with 50 μg SEB were restimulated in vitro with SEB. The peak levels for IL-6 were at 12 hr post SEB exposure while TNF peaked at 6 hr. The percentage of CD4+ cells was significantly increased at 48 hr and 72 hr post SEB (50 μg) administration while the percentage of CD8+ cells remained similar to... [ABSTRACT FROM AUTHOR]