IL-12-induced IFN-γ expression by CD4+ T cells in ILN also declines over 2 to 4 months after primary infection, but the finding that ILN CD4+ T cells collected from mice reinfected 6 months after the primary infection expressed IFN-γ corroborates the establishment and recall of memory within the Th1 cell population. Here, CD4 is linked to infection.