Cell mediated lympholysis in man. Varying strength of the HL-A (LA and FOUR) antigens as sensitizing or target determinants.

The gene products of the LA and FOUR loci of the human Major Histocompatibility Complex (MHC) are generally considered to be a major target in the Indirect Cell Mediated Lympholysis (ICML) test. Within most experiments, a positive correlation exists between the number of HL-A antigens challenged and lympholysis. When different experiments are collated this correlation is less obvious. This discrepancy might be caused by differences between the individual HL-A antigens involved in the afferent phase (MLC) and/or the efferent phase (CML). In 28 experiments involving 97 unrelated individuals we have compared statistically 12 different antigens governed by the LA and FOUR loci. When only one of these antigens is challenged in ICML, target lymphocytes are lysed to different degrees allowing a significant classification of the antigens into different groups, which do not coincide with the classification in the LA and FOUR series antigens. It is concluded that the antigens of the HL-A system are not of equal importance when challenged separately in ICML. The existence of a separate CML locus and a corresponding linkage disequilibrium to the SD loci of the MHC region is suggested.