CD4 and infection: The frequency of IFN-γ production by P25TCRTh1 cells progressively decreasedfrom day 14 to day 42 post-infection, indicating a decrease in the efficiency ofpeptide 25-specific T cell stimulation as infection enters its chronic phase(Figure 3A and 3C).These results with TCR transgenic CD4+ effector cells closelymimic the results observed with endogenous polyclonal CD4+ Tcells after day 14 post-infection (Figure 1B and 1C).