Abstract
Lymph‐node cells (LNC) from multiparous pregnant rats were separated on columns prepared from nylon wool, and tested for cytotoxicity against target tumour cells. Reactivity of LNC towards hepatoma D23 and mammary carcinoma AAF57 was demonstrated in cell populations retained on the nylon wool, and not with cells eluted from the column. Although only 25% of the samples of unfractionated LNC were cytotoxic for tumour cells, retained cell fractions were cytotoxic in 11 out of 12 tests (p = <0.05). Similarly retained LNC were also cytotoxic for 15‐day‐old embryo cells but not for normal adult rat fibroblasts. Using multiparous rat serum it was shown that the reactivity of the retained LNC population could be abrogated in eight out of 11 tests (p = <0.05). The LNC population recovered from the nylon wool constituted 28 to 35% of the original LNC preparation, and consisted of 60–70% Ig‐bearing cells together with a subpopulation of cells responding to soluble PHA. Separation of multiparous LNC on glass beads coated with rat Ig and then rabbit anti‐rat Ig (in excess) also demonstrated the retained cell population to be cytotoxic against tumour cells. Approximately 17–20% of the original cell population was recovered from cells retained on the column, and consisted of an enriched Ig‐bearing cell population (65–80% Ig‐bearing cells) and LNC responsive to PHA. Carbonyl iron treatment of multiparous rat LNC was found to remove detectable cytotoxicity from multiparous rat LNC preparations. The cytotoxicity of multiparous rat LNC retained on nylon wool was also abolished following incubation with carbonyl iron. Definite conclusions as to the nature of the effector cell cannot be drawn from this test, since carbonyl iron treatment was found to remove not only phagocytic cells from LNC preparations but also a proportion of other cell populations including Ig‐bearing lymphocytes. In addition to detecting a cytotoxic LNC population reactive towards tumour‐associated embryonic antigens (retained fraction from nylon‐wool column separation), a subpopulation of multiparous rat LNC was demonstrated in cell fractions eluted from the nylon wool which was shown to suppress the cytotoxicity of the retained multiparous LNC population. The exact nature of this subpopulation of LNC and the mechanism of action is at present not known.