title: The human thymus. II. Partial characterization of thymocytes separated on bovine serum albumin gradients.
abstract: Thymocyte populations from 9 postnatal normal human thymuses (9 mth to 14 yr) were partially characterized after separation from structural elements by mechanical dissociation or spontaneous release from short-term explant cultures. Populations were fractionated on a 17 to 35% discontinuous bovine serum albumin (BSA) gradient and fractions characterized by morphology, pulse labeling index, spontaneous incorporation of labeled thymidine and uridine, E-rosetting ability (4 degrees C) and terminal deoxynucleotidyl transferase (TdT) activity. The following observations were made: (1) the gradient distribution of lymphocytes followed a bell-shaped curve, but with a greater percentage of less dense cells in older thymuses; (2) 60 to 80% of lymphoblasts (3-7% of total thymocytes) were in the 21-23% BSA fractions; (3) spontaneous incorporation of labeled thymidine and uridine was highest in 21-23% fractions; (4) 40 to 55% of lymphoblasts were in active DNA synthesis; (5) less than 50% of lymphocytes from the 17 to 21% fractions formed E rosettes compared to 95% of unfractioned cells; (6) one or two distinct peaks of TdT activity were identified; four thymuses had one peak in the small/medium lymphocyte fractions, whereas in two specimens a second peak was seen. Enrichment of lymphocyte subpopulations of the human thymus for immature cells may aid in further delineation of thymic function in developing man.
mesh_terms: D000375:Aging; D000818:Animals; D002417:Cattle; D002469:Cell Separation; D002499:Centrifugation, Density Gradient; D004247:DNA / Q000096:biosynthesis; D006801:Humans; D008214:Lymphocytes / Q000166:cytology; D009000:Monocytes / Q000166:cytology; D009713:Nucleotidyltransferases / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis; D012397:Rosette Formation; D012710:Serum Albumin, Bovine; D012756:Sheep / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology*
chemical_list: D012710:Serum Albumin, Bovine; D012313:RNA; D004247:DNA; D009713:Nucleotidyltransferases