QUANTITATION AND CHARACTERIZATION OF PLASMA HLA IN NEONATES OF DIFFERENT GESTATIONAL AGES

The functional significance of plasma HLA class I antigens is unclear. They are thought to have an immunomodulatory role and be tolerogenic in transplant settings including the materno-fetal semi-allograft. The re is, however, no available data on the concentrations of soluble HLA class I antigens in fetuses or newborns. We therefore determined plas ma HLA class I antigen levels in 93 neonates born at different gestati onal ages and compared them to those in 66 healthy adults. The mean pl asma HLA concentration in cord blood obtained from these neonates (0.3 0+/-0.15 mug/ml, mean+/-SD) was significantly lower (p<0.0001) than in the adults (0.77+/-0.44 mug/ml). No correlation between the plasma HL A levels and the gestational ages of the neonates was detected. Charac terizing the plasma HLA class I antigens by immunoprecipitation and im munoblotting, four different molecular weight forms, 44, 39, 36 and 34 kDa, were recognized. Their distribution in neonates was not differen t from that in adults. Since the circulating leukocytes are a probable source of plasma HLA class I antigens, we measured the surface HLA ex pression on leukocytes in 4 neonates and 4 adults by immunofluorescent flow cytometry. The fluorescence intensities on neonatal granylocytes and lymphocytes were 50% of those on corresponding adult cells. This finding suggests that the reduced HLA expression by neonatal leukocyte s may be partially responsible for the lower concentration of HLA clas s I antigens in neonatal plasma.