Interaction of thymus lymphocytes with histoincompatible cells. IV. Mixed lymphocyte reactions of activated thymus lymphocytes

CS7BL-activated CBA T cells (T.TDL) were obtained by thoracic duct cannulation of (CBA × C57BL)F₁ mice 4 days after heavy irradiation and injection of CBA thymus cells. T.TDL behaved differently from the TDL of normal CBA mice in unidirectional mixed lymphocyte culture in a number of respects: (a) the response of T.TDL was directed specifically against C57BL antigens, whereas normal TDL responded to both C57BL and BALB/c antigens; (b) the response of T.TDL was rapid but transient compared to that of TDL; (c) whereas only approximately 3% of TDL synthesized DNA specifically in response to C57BL antigens, as many as 25% of C57BL-activated T.TDL responded to these antigens. Evidence is presented which suggests that the T.TDL have a very limited capacity to proliferate. Most of the cells which responded to antigen synthesized DNA without subsequently entering mitosis.     

Physical heterogeneity of mouse thymus lymphocytes.

Mouse thymocytes have been separated by velocity sedimentation in a density gradient. The resulting fractions have been analyzed using electrophoretic light scattering. The electrophoretic distributions of the individual sedimentation fractions reveal the presence of physically distinct subpopulations. Comparison of the mean mobilities of each fraction indicates that the faster-sedimenting cells tend to have a higher electrophoretic mobility.     

Phytohaemagglutinin stimulation of rat thymus lymphocytes glycolysis.

Glucose disappearance and lactate production by the rat thymocytes are stimulated significantly 45 min after addition of phytohaemagglutinin or concanavalin A and the stimulated rate is sustained for at least 8 h. Changes in the steady-state concentration of glycolytic intermediates that occur at non-equilibrium steps during the increased rate of glycolytic flux indicate that the glucose carrier, hexokinase and phosphofructokinase are potentially regulatory steps that undergo nearly simultaneous or tightly sequential activation following interaction of the cells with the mitogen.     

The differentiation of T lymphocytes. I. Proliferation kinetics and interrelationships of subpopulations of mouse thymus cells

Differential quantitative cytotoxic assays were used to distinguish the major high θ population of mouse thymus from the minor low θ subpopulation. The low θ cells were isolated in good yield by killing all high θ cells with controlled anti-θ and complement treatment, followed by a damaged cell removal step. A third population of labile cells, subject to rapid death in culture, was distinguished as a variable component within the high θ category. The corticosteroid sensitivity and anatomical location of these subpopulations was briefly considered. Large and medium sized dividing lymphocytes were studied by pulse labeling with tritiated thymidine, followed by radio-autography of separated subpopulations. Both the high θ and low θ categories included large dividing cells. Kinetic studies under conditions of continuous labeling were used to explore precursor-product relationships among the small thymocytes. Both low θ and high θ small lymphocytes showed continuous and close to linear accumulation of labeled cells, with no evidence for a marked lag in labeling. The turnover time of high θ small lymphocytes was three–four times that of low θ elements. The results suggest largely independent pathways are involved in the development of the two antigenically defined subpopulations. They do not support a direct transfer of “immature” high θ, TL positive small thymocytes in mature, active, low θ,TL negative cells. Some alternative models of T cell development are discussed.     

Characterization of rat bone marrow cells. II. Analysis of surface antigens in small lymphocytes with particular reference to thymus antigen-carrying cells.

Rat bone marrow (BM) small cells were enriched by velocity sedimentation, further separated by means of free-flow electrophoresis, and characterized using T- and B-cell-specific surface markers. More than 80% of these cells were small lymphocytes by morphological criteria and reacted with lymphocyte-specific antisera. A minority of cells had high electrophoretic mobility (EPM), carried surface antigens characteristic of mature T cells, and lacked B-cell markers. These cells may represent recirculating T cells. A small number of cells were found with rat B lymphocyte-specific antigen (RBLA) and surface immunoglobulin (sIg) and had medium EPM. These cell fractions also contained “null” cells which were devoid of T- and B-cell-specific antigens. More than 80% of the BM small cells had low EPM and carried the three subspecificities of the Thy-1 antigen complex and the Thy-A antigens. These antigens were found at several-fold higher concentration on the surface of all thymocytes, but are lacking in most other lymphocytes. The thymus antigen-carrying BM cells of low EPM do not carry other T- and B-cell-specific markers found in thymocytes and peripheral T and B lymphocytes. These markers comprise the T-cell antigens RTLA (rat T-lymphocyte-specific antigen) and RHLA (antigens specific for rat T cells of high EPM) and the B-cell markers RBLA and sIg. Thus the majority of rat BM lymphocytes differ from all other lymphocytes of the T- and B-cell series which makes any classification on this basis purely speculative.     

Fluorescence study of thymus lymphocytes of X-irradiated mice and their progeny.

The mechanisms of changes in the ultra-violet fluorescence (U.V.F.) intensity of mouse thymus lymphocytes 24 hours and 30 days after whole-body X-irradiation have been studied. The thymus lymphocytes of the first generation offspring (F1) from X-irradiated males and unirradiated females were also investigated. At 24 hours after irradiation the U.V.F. intensity decreased for small doses (50 and 65 rad) and increased for doses of more than 100 rad. The changes in U.V.F. intensity were related to a size-independent mechanism. It was found that the U.V.F. increase for doses of 100-700 rad was not connected with the appearance of non-viable (eosin test) cells. The changes in U.V.F. intensity and cellular composition of the thymus were the same 30 days after irradiation and for F1 mice. The increase in U.V.F. intensity was about 14% and did not depend on dose between 50 and 500 rad. About one-half of this increase was connected with an increase in the proportion of medium and large lymphocytes in the thymus. The rest of the effect was related to a size-independent mechanism.