Spleens from tumor-bearing rats contained a population of adherent cells that suppressed lymphocyte responses to Con A and LPS and cell-mediated cytotoxicity (CMC). By use of various fractionation procedures, Ig+ cells, T cells, and null cells were excluded as candidates for the suppressor cell activity. Procedures that removed macrophages abolished the suppressive activity whereas those procedures that enriched for or involved direct addition of macrophages resulted in augmented suppression. On the basis of these results, we conclude that the suppressor elements in spleens of tumor-bearing rats were macrophages.

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This is Publication No. 1082 from Immunopathology, Scripps Clinic and Research Foundation, La Jolla, California 92037. The work was supported by United States Public Health Service Grant AI-07007, AEC Contract AT(04-3)-779, and United States Public Health Service Grant NCI-CB-74-4.

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Copyright © 1976 by The American Association of Immunologists, Inc.
1976
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