Leukocyte complement: assembly of the membrane attack complex of complement by human peripheral blood leukocytes in the presence and absence of serum.

The specific neoantigenic determinants (neoAg) that are indicative of the assembled C5b-9 C complex are generated on the surface of peripheral blood leukocytes (PBL) during collection and processing of blood. Formation of neoAg on PBL could be prevented by collecting blood directly into 20 mM EDTA and, could be induced in vitro by adding autologous serum to isolated PBL that lacked neoAg. When neoAg was induced by the addition of serum containing 125I-labeled C8, the C8 was incorporated into a 23S complex which could be eluted from PBL. A mechanism for neoAg formation on PBL independent of exogenous serum factors was detected when PBL were placed into culture in serum-free medium. Results with metabolic inhibitors and 14C-leucine suggest that PBL can synthesize C5 and assemble the C5b-9 complex. The possible relevance of these findings to the understanding of mechanisms of cell-mediated cytotoxicity is discussed.