The concentration of major histocompatibility complex class II (MHCII), an extracellular complex that presents antigens to CD4+ T cells after phagocytosis, did not change between zero- and three-hours post-infection (16.5 ± 1.6% vs. 14.9 ± 0.4%, p = 0.9966) (Figure 2D). Here, CD4 is linked to infection.