This latter notion is in line with the results of the in vivo BrdU labeling experiment, which show that during the chronic phase of infection, the level of CD4+ T cell expansion in C57BL/6’s is more robust than that in B cell-deficient mice; concomitant with lower lung IL-10 expression in the C57BL/6 mice compared to the B cell-deficient group. Here, CD4 is linked to infection.