Depression of prothymosin-α production in murine thymus correlates with staphylococcal enterotoxin-B-induced immunosuppression

Prothymosin-α (ProTα) and thymosin-β₄ (Tβ₄) were isolated from murine thymus and characterized by microsequence analysis. Murine Tβ₄ has an identical sequence to bovine Tβ₄, whereas murine ProTα is highly homologous to rat ProTα. Murine ProTα differs from rat ProTα at two positions, Glu¹⁰⁰ and Asp¹⁰⁸ of the rat sequence are substituted by aspartic and glutamic acid, respectively, in murine ProTα. The amount of ProTα in murine thymus was found to be reduced after in vivo treatment with staphylococcal enterotoxin-B (SEB), a superantigen which stimulates T cells bearing specific V_β receptors. Results from the anti-SRBC (sheep erythrocyte) plaque-forming cell assay showed that the antibody response of the spleen cells from these animals was also suppressed. On the other hand, the amount of Tβ₄ was not changed significantly. Our studies suggest that the suppression of SEB on antibody response correlates with the depression of ProTα production in the thymus.