Response of HL-A Identical Unrelated Individuals in the Mixed Lymphocyte Culture Test

The immunological responsiveness as measured in the mixed lymphocyte culture test has been studied in 13 pairs of HL-A identical unrelated individuals. In all combinations stimulation occurred and it was frequently of a similar magnitude to that observed against non-HL-A identical subjects. It is postulated that another locus, adjacent to the HL-A locus, is also responsible for the non-stimulation observed between HL-A identical siblings, and that observations made in the related situation should not be transposed to the unrelated situation without some reservation.