Hyporeactivity to mitogens of retroplacental blood lymphocytes in human pregnancy

Retroplacental blood lymphocytes (RPL) obtained from women without complications at the term delivery were studied for proliferative response to mitogens and surface phenotype and were compared with autologous peripheral blood lymphocytes (PBL). Proliferation of RPL induced by phytohemagglutinin (PHA) was significantly lower than that of PBL in 11 of 13 cases. Also RPL proliferated poorly in response to concanavalin A (Con A) in 8 of 10 cases. On the other hand, flow cytometry analysis of T cell subsets revealed that RPL contain comparable or higher number of CD3+ cells and CD4+ cells and similar numbers of CD8+ cells as compared with PBL in most cases. These results indicate that T cell proliferative response in retroplacental space is impaired, which could be due to a functional defect of RPL.