No in vitro evidence for a decreased alloreactivity toward noninherited maternal HLA antigens in healthy individuals.

Pre- and/or perinatal exposure to noninherited maternal HLA antigens (NIMA) is associated with a decreased HLA antibody formation against the NIMA and a significantly better graft survival of kidney grafts from siblings or those from unrelated donors who were mismatched for the NIMA haplotype compared with the NIPA (noninherited paternal HLA antigens) haplotype later in life. These observations suggest that some form of immunological tolerance against NIMA is induced. We analyzed the in vitro T cell reactivity of healthy individuals toward their parents and/or siblings expressing the NIMA or NIPA haplotype to explore whether the alloimmune response to NIMA has distinct characteristics compared with NIPA. No differences were detected by mixed lymphocyte reactions (MLR) and supernatants taken from the MLR showed no differences in IFN-gamma and IL-10 production. Additionally, no differences were found with IFN-gamma and IL-10 Elispot analyses. Phenotypic analysis revealed no selective increase in the number of CD3-CD8dim cells (thought to be a NK-like regulator cell) and the number of CD4+CD25+CD152+ cells (naturally occurring regulatory T cells) after stimulation with NIMA-expressing cells when compared with NIPA-expressing cells. In conclusion, no evidence of an influence of a NIMA effect on the cellular level was found in healthy individuals with "standard" immunological techniques.