Thymic Independence of Adaptive Immunity to the Intracellular Pathogen Shigella flexneri Serotype 2a

Shigella flexneri is a facultative intracellular pathogen. While immunity to several intracellular pathogens is mediated by T lymphocytes, it is unknown whether cellular immune responses are important to adaptive immunity to S. flexneri. We show that vaccination with S. flexneri serotype 2a confers protection to mice that lack T lymphocytes or gamma interferon (IFN-γ), specific depletion of T lymphocytes does not alter the protection, and adoptive transfer of splenocytes from vaccinated mice does not confer protection to naive mice. In contrast, vaccination conferred no protection to mice that lack B lymphocytes and adoptive transfer of immune sera conferred partial protection to naive mice. These data demonstrate that in the mouse bronchopulmonary model, adaptive immunity to S. flexneri 2a is an antibody-mediated, B-lymphocyte-dependent process and can be generated in the absence of T lymphocytes or IFN-γ.