CD4 and infection: Upon challenge infection, elevated IgG- and IgA-secreting plasma cells, germinal center B cells, and memory B cells were observed, and CD4<sup>+</sup>, CD8<sup>+</sup> T-cells, as well as both Th1 (IFN-γ) and Th2 (IL-4, IL-5) cytokines, were also increased.