CD4 and infection: The mouse infection model has allowed the discovery of some parasite enzymes that affect the physiology of CD4+ T cells in diverse ways, constituting potential evasion mechanisms: two enzymes from the trans-sialidase family (a proper trans-sialidase and another one lacking this activity), inhibit their expansion and promote a TH2 cytokine profile, as authors observing a decrease in the secretion of IFN-γ and an increase in that of IL-4 suggest.