Genetic Analysis of HLA-D Region Products Defined by PLT

The finding that in vitro human primed lymphocytes (PLs) can function as memory cells allowed the analysis of genetic questions which had previously required in vivo immunizations [1]. It seemed it would be a simple task to clarify the polymorphic system of the HLA-D “locus” by priming against determinants encoded by a single haplotype [2], since the main responsibility of this locus for proliferation in primary mixed lymphocyte culture (MLC) [3] was demonstrated also in secondary MLC in an HLA-B: D recombinant family [4]. Despite the good correlation found between determinants defined by haplotype PLs and HLA-D homozygous typing cells (HTC), some evidence suggested that at least two antigenic systems encoded by one HLA haplotype were recognized by PLs [5, 6]. A considerable contribution to the strength of PL responses by products encoded by loci telomeric to HLA-DR/Dw was also shown in HLA-B: D recombinant families [7, 8].