Analysis of the in vivo dendritic cell response to the bacterial superantigen staphylococcal enterotoxin B in the mouse spleen

To investigate the in vivo effects of Staphylococcal enterotoxin B (SEB) on dendritic cells (DCs) in the spleen, a single dose of SEB (50 mug/kg) was administered to BALB/c mice by intraperitoneal injection. Afterwards, the m ice were sacrificed at 2, 6 and 24 hr, 2, 4, 7 and 15 days, and the spleens were removed. The immunocytochemical characterization of the cells was car ried out using various monoclonal antibodies in cryostat-cut sections. The distribution patterns of DCs and their major costimulatory molecules, C D80, CD86 and CD40 in the spleen were identified, and the evidence for matu ration of DCs in vivo in response to SEB was obtained. It was found that sy stemic administration of SEB induced the migration of most of the immature, splenic DCs from the marginal zone to the periarterial lymphatic sheath wi thin 6 hr. This movement paralleled a maturation process, as assessed by up regulation of CD40, CD80 and CD86 expression in the interdigitating dendrit ic cells (IDCs). The upregulation of costimulatory molecule expression was conspicuous only in DCs in contrast to other antigen-presenting cells (APCs ) such as macrophages and B cells which did not show any significant altera tions in their costimulatory molecule expression. We also demonstrated the temporal expression pattern of these costimulatory molecules on the activat ed DCs. The upregulation of costimulatory molecules on DCs reached a peak l evel 6 hr after SEB injection, while the increase in number of T cells expr essing T cell receptor V beta8 reached a peak level on day 2 after SEB trea tment. In conclusion, we demonstrated the in vivo DC response to SEB in the mouse spleen, especially a potent stimulative effect of SEB on DCs in vivo, a tem poral distribution pattern of DCs as well as T cells including TCR V beta8( +) T cells, and a differential expression pattern of costimulatory molecule s on the activated DCs. The results of the present study indicate that DCs are the principal type of APCs which mediate T cell activation by SAg in vi vo, and that each costimulatory molecule may have different role in the act ivation of DCs by SAg. Thus, it is plausible to speculate that DCs play a c ritical role in the T cell clonal expansion by SAgs and other SAg-induced i mmune responses in vivo.