DIFFERENTIATION OF IMMUNOLOGICALLY SPECIFIC CYTOTOXIC MACROPHAGES INTO TWO TYPES ON THE BASIS OF RADIOSENSITIVITY

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Abstract

SUMMARY

Macrophages which are cytotoxic in vitro to tumour cells in an immunologically specific manner can be classified into (1) radiosensitive, cytotoxicity totally abolished by 500 R of X-rays; and (2) radioresistant, cytotoxicity unaffected by 500 R but partially ablated by 1,000 R. Radiosensitive macrophages are found in both syngeneic and allogeneic mice immunized with radiation-killed lymphoma cells. Radioresistant macrophages are produced by immunizing mice with allogeneic living lymphoma cells. In a syngeneic system radioresistant macrophages are produced when mice, which have first been rendered immune by immunization with radiation-killed cells, have rejected an inoculation of living cells. Immune or armed macrophages which have been rendered nonspecifically cytotoxic (i.e., “activated ” by incubation with the antigen to which they are sensitized) or normal macrophages activated by treatment with endotoxin show very great resistance to irradiation and retain activity after exposure to 5,000 R in vitro.

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