Mechanisms of long and short term immunity to plague.

Long and short term immunity to plague was produced in normal mice by using, respectively, an antibiotic resistant Yersinia pestis and Yersinia pseudotuberculosis. Both immunogens were used live. Passive serum transfer experiments, together with assays for the bactericidal activity of macrophages and delayed hypersensitivity tests, showed that the short term immunity was of a humoral nature and the long term immunity was cell mediated. The plague virulence markers of the two immunogens were: Y. pestis VW- F1+ P1+ P+; Y. pseudotuberculosis VW+ F1- P1- P-. The challenge organism was Y. pestis VW+ F1+ P1+ P+.