Comparison of soluble and membrane bound HLA-class I and DR levels in umbilical cord blood and adult peripheral blood.

HLAs are membrane bound (membrane HLA mHLA) or secreted as soluble forms(soluble HLA = sHLA) in plasma or serum. Umbilical cord blood (UCB) mHLA, from mononuclear cells (MNCs), and sHLA were quantified by flow cytometry and enzyme linked immunosorbant assay (ELISA), respectively, and compared to levels of MNC-mHLA and sHLA in adult peripheral blood (PB). The mean fluorescence intensity (MFI) of mHLA-I was 3-fold lower in UCB-MNCs than in adult PB-MNCs, however, due to higher cell numbers in UCB, total mHLA-I quantities per ml of blood were not different in UCB and adult PB. In addition, sHLA-I in UCB was significantly lower than in adult PB. The MFI of mHLA-DR from UCB-MNCs was significantly higher than the MFI of mHLA-DR in adult PB-MNCs, and the total mDR quantity (per ml of blood) in UCB was 3-fold higher than in adult PB. sHLA-DR concentrations, however, were equivalent in UCB and adult PB. These findings indicate that fetal tissue or cells might excrete smaller quantities of both sHLA-I and sDR antigens than adult tissues or cells. Alternatively, fetal sHLA antigens might be unstable and degradated compared to those of adult.