An Antigenic Marker for Human Thymic Lymphocytes

Murine thymocytes and thymus-derived lymphocytes possess antigens not normally represented on most other tissues. Antigens of the TL (1), Ly (2), and θ (3) systems can be detected by isoimmunizations with mouse strains differing at the appropriate genetic locus. By immunization of rabbits with mouse lymphoid cells, followed by appropriate absorption procedures, reagents have been produced which can also identify and selectively lyse several different lymphocyte populations (4–6). The availability of immunologic reagents for detecting antigenic differences has greatly facilitated investigations of functional differences among subpopulations of mouse lymphocytes. Similar reagents have not been available previously for the study of human lymphocyte subpopulations. We have investigated the usefulness of absorbed heterologous antihuman thymocyte serum for the detection of antigenic heterogeneity in human lymphoid cells. Thymus cells were obtained from fetuses and from infants under 1 year of age. Rabbits were injected in the foot pads with 109 cells emulsified with complete Freund's adjuvant. They were given an intravenous injection of 10 9 cells on day 14 and were bled on day 21. Those sera showing a high titer of complement dependent antibody against human peripheral blood lymphocytes were pooled, and the gamma, globulin was precipitated with ammonium sulfate. The precipitate was made up to a concentration of 8 mg/ml in saline containing 30% v/v human albumin. All sera were Millipore filtered and stored at –20°C.