Figure 1.

Hypothesis on generation of the memory T cell population in reproduction through paternal-fetal antigen exposure. Firstly, naive T cells are exposed to the male antigen through antigens in seminal fluid. A subsequent encounter with the antigens occurs during pregnancy through exposure to fetal antigens on trophoblast cells and through microchimerism. Postpartum, the maternal immune system remains exposed to fetal antigens through microchimerism. In addition, postpartum, memory T cells are possibly exposed to paternal antigens through exposure to seminal fluid. In a subsequent pregnancy, the maternal memory T cells likely reaccumulate and respond to the cognate paternal-fetal antigens.