ABSTRACT
In man, the discovery of the "Ia" equivalents followed a different course than that in the mouse. In experimental animals, the I-region was defined by immune response (IR) genes and the Ia antigens were found as a result of the attempt to define the gene products of the IR genes. Since the procedure of typing for HLA-D with homozygous typing cells is rather cumbersome, time consuming, and not always easy to interpret, attempts were made to define mixed lymphocyte culture (MLC) antigens by serologic means. A number of serological problems can cause considerable variations of DR typing results. One important variable is the quality of the antisera. Antisera containing anti-HLA-DR antibodies can be obtained from multiparous women and from patients who have been repeatedly transfused. One of the most intriguing observations in HLA serology is the extensive cross-reactivity found for alleles coded for by the same locus.
