Confounding factors in HLA-DW 2 typing of human leucocytes

Three healthy HLA-B7 homozygous subjects were found with similar but not identical HLA-D antigens; one was DW 2 homozygous according to independent typing results. This could be an expression of "long" and "short" HLA-D antigens or be due to differences in weak antigens outside the HLA-D region. Two further healthy HLA-B7 homozygous subjects were studied; one was apparently heterozygous for DW 2, the other apparently carried no DW 2 antigen. Both could discriminate between different DW 2 homozygous test cells. Two such test cells--one from a patient with multiple sclerosis (MS) and the other from a man with two children with MS--gave variable and absurb reactions with cells from the two subjects in question. It is tentatively suggested that genes exist which, when present in both moities in a mixed leucocyte reaction (MLR), can impair the MLR and give false "typing" reactions. This might be more common among patients with MS and perhaps also some other diseases (certain arthritides, e.g. rheumatoid arthritis) than among healthy subjects and can complicate or make impossible the interpretation of HLA-D typing data. It could also explain the previously-described impaired MLR between cells from patients with these diseases.