CD4 and infection: Shown is the effect of B. burgdorferi infection on the abundance (percentage of all human CD45+ cells) and activation status (CD69 expression) of human CD19+ B cells (A-C), CD33+ myeloid cells (D-F), CD4+ T cells (G-I), and CD8+ T cells (J-L) in the peripheral blood (PBL), spleen, and left and right joints 38 days after infection.