Early expression of cytokines in lymph nodes after treatment in vivo with Staphylococcus enterotoxin B

Excessive cytokine expression induced by superantigen may be one aspect of the pathophysiology associated with Gram positive bacteremia. We have undertaken a study of the kinetics of cytokine production in lymph nodes obtained from in vivo Staphylococcus enterotoxin B (SEB) treated animals. This study was designed to evaluate the short term cytokine profile observed using immunohistochemistry (IHC) in BALB/c mice injected intraperitoneally (i.p.). The observed immunohistochemical kinetic profiles were corroborated using reverse transcription-polymerase chain reaction (RT-PCR) RNA analysis. We report here that TNF, IL-2, and IFN-gamma are the principal cytokines which were detected within hours of SEB administration, and that other cytokines such as IL-3, IL-4, IL-5, IL-6, IL-10, GM-CSF and M-CSF were undetectable. TNF and IL-2 appeared very early following SEB priming, and were observed by 1 h. IFN-gamma which appeared later (maximally at 14 h) was produced predominantly by CD8+ cells. In contrast, the TNF and IL-2 were produced primarily by CD4+ cells. Identical results were obtained by IHC and RT-PCR; the kinetics of mRNA expression slightly preceded the appearance of protein. The TNF and IFN-gamma staining patterns observed in lymph node sections were indicative of Golgi-localized cytokine. The IL-2 staining pattern observed in lymph node sections was distinctive, covering a significant local area of cells. This local regional concentration of IL-2, which may result from cytokine attached to extracellular binding components, may be an important aspect of the activation phase of a developing immune response. Rapid induction and excessive cytokine production elicited by superantigen in vivo, may ultimately help to explain the shock and death associated with SEB.