An immunohistochemical study of leucocytes in human endometrium, first and third trimester basal decidua

An immunohistochemical quantitative study of leucocyte subpopulations on fresh human endometrium and on biopsy specimens of first and third trimester basal decidua in normal (uncomplicated) pregnancies was performed. The most prominent population in endometrial and decidual stroma of basal decidua are macrophages. B cells as well as gamma/delta T cell receptor positive cells were found occasionally, scattered throughout the endometrial/decidual stroma. CD3+ cells were present in a relatively small number in the endometrium as well as in the first trimester basal decidua, but their number was elevated (doubled) in the third trimester of pregnancy. CD2+ cells showed a slight increase in first trimester basal decidua when compared with both endometrium and third trimester basal decidua. Cells with positive NKH-1 marker (CD56+) showed a significant increase in the first trimester, while in the third trimester their number diminished drastically. CD56:CD3 cell ratio increased to more than five times in first trimester basal decidua, while in the third trimester basal decidua decreased drastically. The mentioned increase of CD56+ cells in the first trimester and that of CD3+ cells at term suggests that these cells could have some specific function(s). However, it still has to be established whether the described quantitative changes of decidual leucocytes in basal decidua during pregnancy are of any importance for the mechanism(s) for the fetal allograft protection.