To detect the cellular origins of α-lymphotoxin (α-LT), we cultured various subpopulations of human blood lymphocytes separated by erythrocyte-rosetting techniques with various mitogens. T cell-enriched subpopulations responded to PHA by increased 3H-thymidine uptake into DNA and large amounts of α-LT production. SPL and Con A-Sepharose stimulated DNA synthesis in T cell-enriched cultures if the macrophage content was greater than 1.5%; however, α-LT production was not induced by these two mitogens even when reconstituted with 10% macrophages. B and/or null cell-enriched populations severely depleted of T cells (less than 0.7%) did not respond to PHA, SPL, or Con A-Sepharose. However, reconstitution to 5 or more percent in E-RFC allowed all three mitogens to stimulate DNA synthesis and α-LT production. The LT made by all cell populations 5 and 7 days after stimulation were equally neutralized by a heterologous antiserum to α-LT. These results show that human T and B and/or null cells, when appropriately stimulated, can produce α-LT.

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