COLOCALIZATION OF BETA-2-MICROGLOBULIN AND IGG IN HUMAN PLACENTAL SYNCYTIOTROPHOBLASTS

The fetal syncytiotrophoblast cells in close contact with maternal blo od circulation apparently lack surface expression of HLA molecules, in cluding the HLA light chain beta 2-microglobulin. This is thought to c ontribute significantly to a successful pregnancy. We find that syncyt iotrophoblasts do express beta 2-microglobulin. beta 2-microglobulin i s primarily localized intracellularly in apical granules, and co-local ize with human IgG. The origin and function of syncytiotrophoblast bet a 2-microglobulin is unknown, but its localization in the syncytiotrop hoblasts may implicate beta 2-microglobulin in the transplacental tran sport of IgG in conjunction with a recently identified class I HLA-lik e receptor for IgG/Fc. Alternatively, beta 2-microglobulin may associa te with a hitherto unidentified class I HLA molecule.