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. tu larensis live vaccine strain (LVS), the role of B cells themselves in prima ry and secondary infection with such bacteria has not been examined directl y. We show here that mice deficient in mature B cells and antibodies (B-cel l knockout mice) are marginally compromised in controlling primary subletha l infection but are 100-fold less well protected against secondary lethal c hallenge than are their normal counterparts. This defect in optimal specifi c protective immunity uas readily reconstituted by the transfer of primed, and to a lesser degree, unprimed B cells, but not by the transfer of specif ic antibodies. The results indicate a previously unappreciated role for B c ells in secondary immunity to intracellular pathogens through a function ot her than antibody production.