Serological studies of HL-A on continuous lymphoblastoid cell lines (CLC) and the definition of an antigen on CLC determined by a heat-labile antibody.

Continuous lymphoblastoid cell lines (CLC) are more reactive with HL-A antisera in a complement-dependent cytotoxic test than are peripheral blood lymphocytes (PBL). This additional reactivity leads to assignment to a given CLC of more than four HL-A antigens, the maximum allowable under the two locus concept of the genetic control of HL-A. However, absorption of antisera by CLC shows that no more than four HL-A antigens exist on any of the CLC used in this laboratory. The additional reactivity of these cells lines can be explained in three ways. Firstly, it may be due to the presence of sublytic amounts of HL-A antibody in operationally monospecific antisera. Secondly, it may be due to cross-reactivity between HL-A antigens. Both these findings can be explained on the basis of the increased quantity of HL-A antigens on CLC compared to PBL. Thirdly, it may be due to the presence of a heat-labile (56° for 30 min) complement-dependent cytotoxic antibody which is present in 90% of normal human sera, and detects an antigen group tentatively labelled `D'.