Lectin separation of nonlymphoid suppressor cells induced by total lymphoid irradiation

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Abstract
Suppression of the mixed lymphocyte reaction (MLR) exerted by splenocytes derived from mice treated with fractionated total lymphoid irradiation (TLI, 200 rds × 8) was analyzed by various criteria in order to characterize the phenotype of the cell type(s) responsible for suppression. TLI‐induced suppressor cells could not be eliminated by removal of cells bearing surface immunoglobulin, Thy‐1, Lyt‐2 and TL, and thus could not be ascribed to lymphocytes of the B or T cell lineage. Suppressor cells were large, and nonadherent to nylon wool, Sephadex G‐10 and plastic surfaces. Suppressor activity of TLI splenocytes was predominantly located in fractions of cells bearing receptors for soybean agglutinin (SBA), peanut agglutinin (PNA) or both lectins. SBA+, PNA+′, sequentially agglutinated (SBA followed by PNA) SBA+PNA+ and (PNA followed by SBA) PNA+SBA+ suppressor cells were radioresistant upon exposure to 1000 rds in vitro. Cells bearing the receptor for PNA but lacking that for SBA (PNA+SBA−) had sharply reduced suppressor activity. However, a radiosensitive PNA− suppressor cell subset was also documented in the spleen of TLI‐treated mice. Thus, suppressor cells could best be physically separated from nonsuppressors by the SBA lectin. SBA+ suppressor cells were found, by scatter analysis, to include the population of large cells characteristic of TLI splenocytes, whereas SBA− cells were much smaller and almost exclusively devoid of suppressive capacity. The PNA receptor was found to further dissect the SBA+ suppressor cells into two distinct subpopu‐lations: radioresistant SBA+PNA+ cells and radiosensitive SBA+PNA− cells. In summary, we suggest here the presence of at least two suppressive populations induced by TLI: (a) radioresistant SBA+, PNA+, SBA+PNA+ or PNA+SBA+ cells, and (b) radiosensitive PNA− and SBA+PNA− cells. Similar subsets of MLR suppressor cells can be isolated from normal bone marrow cells and splenocytes of nude mice, suggesting that suppression is mediated by large, immature, nonlymphoid cells which might migrate from shielded bone marrow compartments into the spleen of TLI‐treated mice.