Human thymocytes (THY) were examined for the expression of HLA-A,B,C antigens on their cell surface by using tissue typing alloantisera in the microcytotoxicity assay. Approximately 80% of the total THY population demonstrated antibody-mediated, C-dependent lysis with several alloantisera for each HLA-A,B,C specificity. The HLA phenotype of THY was verified by HLA typing autologous peripheral blood lymphocytes (PBL) from the thymus donor. Thymus tissue and PBL were obtained from cardiac surgical patients ranging in age from 3 mo to 12 yr. The capacity of THY to absorb HLA alloantibody was also demonstrated. Cross-absorption studies performed on PBL and THY by using HLA typing sera produced two important findings: 1) HLA typing sera that are devoid of non-HLA THY-specific antibody can be used to HLA type THY and 2) selected non-HLA sera from multiparous women, and selected HLA typing sera absorbed with PRL or platelets can be used to detect THY differentiation antigens. Taken together, cytotoxicity data, absorption capacities, cross-absorption studies, and statistical analysis indicate that HLA-A,B,C alloantigens and non-HLA polymorphic differentiation antigens detected by alloantisera are co-expressed on the cell surface of the majority of human THY.

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