Importance of B cells, but not specific antibodies, in primary and secondary protective immunity to the intracellular bacterium Francisella tularensis live vaccine strain.

Although there appears to be little if any role for specific antibodies in protection against intracellular bacteria, such as the model pathogen F. tularensis live vaccine strain (LVS), the role of B cells themselves in primary and secondary infection with such bacteria has not been examined directly. We show here that mice deficient in mature B cells and antibodies (B-cell knockout mice) are marginally compromised in controlling primary sublethal infection but are 100-fold less well protected against secondary lethal challenge than are their normal counterparts. This defect in optimal specific protective immunity was readily reconstituted by the transfer of primed, and to a lesser degree, unprimed B cells, but not by the transfer of specific antibodies. The results indicate a previously unappreciated role for B cells in secondary immunity to intracellular pathogens through a function other than antibody production.