Serological detection of B-cell ("Ia-like") antigens in serum of normal donor and in some sera of leukaemic patients.

Some sera from normal donors (1/18) and from leukaemic patients (2/7 with acute myeloid leukaemia [AML], 1/4 with chronic lymphatic leukaemia [CLL], 0/3 with acute lymphoblastic leukaemia [ALL]; with high numbers of leukaemic cells expressing Ia-like p28,33 antigen on the leukaemic cell surface) inhibited the complement mediated cytotoxic activity of highly specific xenogenous anti Ia-like sera (which were prepared by immunization of rabbits with insoluble membrane fractions of B-type lymphoid lines) at a titre 1:4 or less. This effect was not observed with antisera directed against other membrane marker determinants (e.g. T lymphocyte specific antigens). These results suggest that at least a small proportion of membrane bound Ia-like antigens can be released from cell surfaces and in some patients these Ia-like moieties are detectable (by sensitive inhibition assays) in the serum.