THE NATURE OK BLOOD-BORNE CYTOTOXIC CELLS

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Abstract
SUMMARY Ten days or more alter sheep had been immunized s.c. with murine lymphoma cells, cytotoxic white cells were present in the blood but were absent from intermediate lymph. This cytotoxic activity did not require complement and was not reduced by exposing the blood cells to 500 It of X-irradiation; it was abolished by the removal of glassadherent cells, or by treatment with antimaerophage serum. Alt hough lymphocytes from intermediate lymph of immunized sheep were not cytotoxic, themselves, they were able 1o confer cytotoxic activity on white cells from the blood of unimnninized sheep. Similarly, lymph-borne lymphocytes from immunized sheep could confer cytotoxic activity on monolayers of macrophages obtained from the udders of normal ewes. When lymph cells from an immunized sheep were incubated in vitro with irradiated lymphoina cells, a soluble factor was released into the supernatant which induced cytotoxic activity in the white cells from the blood of normal sheep. It, was concluded that, alter immunization the regional nodes release a population of lymphocytes that are sensitized but not cytotoxic. When such cells reencounter the antigen they produce a factor which induces cytotoxieitv in a subpopiilation of mononuclear effector cells which are present in blood and peripheral tissues but not in intermediate, lymph. There is compelling circumstantial evidence thai these effector cells belong to the monoeyte-macrophage series, but at present we prefer to describe them merely as blood-borne cytotoxic cells.

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