Non-cytotoxic alloantibodies defined by the EA rosette inhibition assay

Sera from both transfused individuals and pregnant women mediated inhibition of Fc-rosette formation. Both normal blood B lymphocytes and chronic lymphocytic leukemia cells were used as targets. Inhibition was not related to the presence or absence of lymphocytotoxic antibodies. When tested against a panel of B lymphocytes these sera displayed selective reactivity in keeping with the recognition of allospecific determinants. No association between the target antigen(s) and classically defined MHC-coded structures was evident. Heteroantibodies to both class I and class II MHC structures as well as beta 2-microglobulin also mediated FcR blockade. However, unlike the alloantisera tested, these antibodies displayed no restriction in their reactivity toward individual target cells.