The thymus is essential to the development of cell-mediated hypersensitivity as well as certain types of antibody formation (1–3). An interaction of thymus-derived and bone marrow-derived cells apparently is required for many of these responses (4–8). In cases studied thus far which involve hemolysin production against sheep erythrocyte antigens, thymus-derived cells show an initial mitotic response to the antigenic stimulus, but the actual antibody-forming cells have proved to be marrow-derived (5–8). In tuberculin hypersensitivity, which may be taken as a well-established example of cellular hypersensitivity, while the thymus is required for active sensitization the overwhelming majority of cells which leave the circulation and infiltrate specific delayed skin reaction sites are nonspecific marrow-derived monocytes (9–11). The data presented here establish the presence of significant proportions of thymus-derived cells in the early stages of the tuberculin reaction in the rat. The animals, materials and techniques used in this study have been described in detail elsewhere (10, 12). Male Lewis rats were thymectomized at 5 weeks of age and x-irradiated (900 rads) 2 to 3 weeks later. Within a few hours of irradiation 2 × 108 adult Lewis bone marrow cells were injected intravenously, and on the following day each animal was grafted subcutaneously with pieces of thymus from two 5- to 7-week-old (Lewis × DA)F1 hybrid donors. Ten to 13 days after thymus grafting, each rat received 1.0 mg heat-killed tubercle bacilli in oil (complete Freund’s adjuvant) injected into the four footpads. After 10 to 15 days, duplicate skin sites were injected with 50 µg purified protein derivative (PPD, Parke, Davis & Co.) and with 20 % turpentine (redistilled artists’ rectified turpentine) in mineral oil. Variation in the intervals separating thymus grafting, immunization, and skin testing did not affect the results; corresponding data were therefore pooled. Groups of 7 to 10 rats were killed 8, 16, and 24 hr after skin testing. Cell suspensions made from the spleen, lymph nodes, and delayed skin reactions in individual animals were subjected to immunofluorescence analysis. Lewis anti-DA isoantisermn was used to identify hybrid (thymus-derived) cells and normal Lewis serum was used as control. Fluorescein-conjugated rabbit anti-rat immunoglobulin stains 100% of living DA or (Lewis × DA)F1 cells previously incubated with Lewis anti-DA but less than 2% of cells after prior incubation with normal Lewis serum. In almost all eases 100 to 200 living cells were counted.
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Williams et al. (1969) studied this question.