Anomalous Mixed Lymphocyte Culture Reactivity between HLA—A, —B, —C, —DR Identical Siblings

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Abstract
Complete HLA typing including HLA-A, -B, -C, -DR (D related B [bone marrow-derived] cell typing), -D, mixed lymphocyte culture (MLC), and primed lymphocyte testing (PLT), together with complete red blood cell (RBC), glyoxalase (GLO), GBG (Factor B) and phosphoglucomutase 3 (PGM3) typings were performed on an informative family. The 5 siblings inherited the 4 possible combinations of parental HLA haplotypes, and 2 of the siblings were HLA-A, -B, -C and -DR identical. Repeated MLC testing of the family revealed positive mixed lymphocyte reactivity in all combinations. B cell typing for the DR specificities demonstrated no variation from the expected inheritance pattern and specifically no recombination event. GBG and GLO typings militated against a recombination involving the paternal chromosome. HLA-D testing revealed that only 1 of the HLA-A, -B, -C and -DR identical siblings gave typing responses to the HLA-Dw3 specificity present on that maternal haplotype. Utilizing HLA haploidentical combinations, lymphocytes were primed against the 4 parental haplotypes and the non-Dw3 haplotype of interest (Aw24-B8-DRw3-LDY) in the PLT. The sibling inheriting this haplotype did not restimulate cells primed against the A2-B40-DRw6-LDY specificity. No discrimination was observed in the restimulation of lymphocytes primed against this haplotype. Possible interpretations of these family data include: a spontaneous mutation, non-major histocompatibility locus (MHC) stimulation and HLA-DR/D recombination.