"Bare lymphocytes" without immunodeficiency

"Bare lymphocytes," which cannot be typed for the HLA-A,B, and C antigens were observed in two siblings, nine and six years of age. The elder child presented with aplastic anemia and was being considered for bone marrow transplantation. The younger child was healthy. The inability to phenotype both children for these three gene products persisted throughout the 21-month period of observation. The DR antigens were demonstrable which rendered it possible to deduce their A, B, and C genotype from the typing of the other four family members. Although alloantisera failed to detect the antigens on peripheral blood lymphocytes, monoclonal antibodies demonstrated reduced amounts of the HLA-A,B, and C antigens on the cells. The reduced level was confirmed following EBV transformation of the cells. After prolonged culture, HLA antigens immunoprecipitated from the cell extracts were normal in amount, molecular weight, and polypeptide composition. Southern blot analysis did not reveal gross genomic rearrangements. A regulatory defect leading to the expression of these Class I antigens is postulated.