HUMAN CYTOTROPHOBLASTIC CELLS ABSORB THE NK BLOCKING ACTIVITY OF MONOCLONAL BA11

PROBLEM: R80K is a polymorphic alloantigeneic protein present on human placental trophoblast and on paternal B lymphocytes and monocytes. Th is protein, unlike the former candidate TLX antigen, stimulates a prot ective maternal immune response in vivo. A murine monoclonal BA11 anti body, directed against R80K, prevents abortion in three murine pregnan cy-failure models and inhibits human and murine NK activity. We attemp ted to define the target of BA11 in the human NK assay system. METHODS : A CELISA method was used to detect R80K antigen on the surface of di fferent cells using the BA11 antibody. The effect, on human peripheral blood NK activity against K562, by BA11 before and after absorption b y different cells, including the K562 target, was determined. RESULTS: R80K was detected on term placental syncytio and cytotrophoblast and on BeWo cells, by CELISA. BA11 suppressed NK lysis of K562 cells in a dose-dependent manner. Absorption of the BA11 by BeWo and by cytotroph oblastic cells significantly decreased the NK-inhibitory activity, The re was minimal absorption by K562 and BA11-pretreated K562 cells remai ned susceptible to NK lysis. By contrast, BA11-pretreated peripheral b lood cells lost all NK activity. CONCLUSIONS: The inhibition of NK kil ling of K562 cells by BA11 is more complex than a simple masking of a trophoblast cell-associated molecule in K562 necessary for recognition in NK cells.