Characteristic changes of large granular lymphocytes that strongly express CD56 in endometrium during the menstrual cycle and early pregnancy

Large granular lymphocytes that strongly express CD56 (CD56(++) LGL) constitute a major population of leukocytes in the secretory endometrium and pregnancy decidua and are considered to be involved in reproductive immunity and in maintaining the pregnancy. The present study aimed to reveal the relationship between the characteristic changes of CD56(++) LGL and altered hormonal environment and/or trophoblast invasion in the endometrium. Cell surface markers of CD56(++) LGL obtained from the endometrium during the menstrual cycle and early pregnancy were analysed using how cytometry, The percentages of both CD56(++) LGL that express activation antigens (CD69, HLA-DR) and those that express lymphocyte function associated antigen-1 (LFA-1) (CD11a/CD18) were highest in the proliferative phase and decreased gradually throughout out the menstrual cycle. Expression of these antigens was further suppressed in the late secretory phase, as well as in the early stage of pregnancy. However, the percentage of CD56(++) LGL that express these antigens was significantly higher in spontaneous abortions than in normal pregnancies. On the other hand, the percentage of CD56(++) LGL that express CD45RA was lower during normal pregnancy than during the menstrual cycle. The present results suggest that characteristics alterations of CD56(++) LGL are regulated by altered hormonal environment and by trophoblast invasion.