CD4 and infection: Interestingly, our previous study (33) also demonstrated that PIV conferred i) comparable levels of protection against NMI infection in WT, CD4+ T cell-deficient, and CD8+ T cell-deficient mice; ii) partial protection against splenomegaly but no protection against bacterial replication in T cell-deficient mice; and iii) no measurable protection in B cell-deficient mice.