Strong mixed lymphocyte reaction associated with the LA or first locus HL-A

Bidirectional strong stimulation in one-way mixed lymphocyte cultures (MLC) is reported between an HL-A recombinant and sibling, apparently differing only at the LA or first locus HL-A. The strong MLC reaction may represent a second strong MLR-S locus associated with the LA or first locus HL-A. Alternative explanations are discussed. A second example of a recombinant HL-A haplotype transmitted to progeny is also reported.