Time course analysis of alpha+ beta+ T cell clones during normal pregnancy.

During normal pregnancy, the fetus continues to mature inside the uterus without rejection. Inherited paternal antigens could be targeted by the maternal immune system. These reactions are believed to play a role in a number of habitual abortions. However, the precise maternal mechanisms preventing fetal tissue rejection are not well understood. Maternal T cells should recognize fetal antigens, so it is conceivable that antigen-specific T cell response to fetal antigens would occur by proliferation and accumulation of certain T cell clones in the pregnant mother. To elucidate the maternal immune response to the fetus we investigated the clonality of expanded T cells in peripheral blood lymphocytes in ten normal pregnant women. We employed reverse transcriptase-polymerase chain reaction for T cell receptor beta chain gene and subsequently analyzed the PCR product by single-strand conformation polymorphism analysis. A large number of distinctly expanded T cell clones were detected during pregnancy. These accumulations were observed as early as the ninth to tenth week post-conception and reached a maximum during the second trimester, suggesting the existence of dynamic antigen-specific T cell responses in the pregnant mother. However, after the 30th week of gestation, nearly all expanded T cell clones disappeared before parturition and the degree of clonality reached almost normal levels. Our results clearly indicate the existence of dynamic maternal T cell responses during pregnancy.