CD40LG and susceptibility to pneumonia measurement: Despite the clinical importance of respiratory pathogens especially in immunosuppressed subjects, at present, there are limited data on the consequences of the different modalities of B cell depletion on antibody-mediated immunity to S. pneumoniae. In this study, we have developed a mouse model of B cell depletion and tested the consequences of low levels of B cells on natural IgM and the development of colonization induced antibody mediated immunity to S. pneumoniae to subsequent pneumonia challenge.