Luteinization of human granulosa cells in vivo is associated with expression of MHC class II antigens.

We previously described the presence of MHC class II (HLA-DR) antigens, structurally similar to those on lymphoid cells and bearing the genetically-appropriate allotypic determinants, on human adrenocortical cells in the zona reticularis of normal glands. We now report a similar expression by granulosa-lutein cells (GLC) in corpora lutea (CL) of normal ovaries, as detected by indirect immunofluorescence techniques with the use of mouse monoclonal antibodies (MAb). In some cases, GLC were also positive for HLA-DQ and -DP antigen expression. Neither granulosa nor theca interna cells in large antral follicles of the same ovaries showed any detectable expression of MHC class II antigens. Moreover, theca-lutein (paralutein) cells, identified by their reactivity with specific human autoantibodies in 5 of the 7 human CL examined, were also negative. Similarly, GLC, but not paralutein cells, in rhesus monkey CL showed significant cross-reactivity with anti-HLA-DR MAb. In contrast, lutein cells in ovaries from either cycling or 7-day-pregnant rats were negative for MHC class II (Ia) antigen expression. Expression of MHC class II antigens by human granulosa cells after their luteal transformation confirms the normal inducibility of certain human steroidogenic cells at the time of their further functional differentiation and enhanced biosynthetic activity, and suggests that these molecules may have additional functions beyond serving as restriction elements in the immune response.