Leukemia in AKR mice: a defined suppressor cell population expressing membrane-associated DNA

Leukemic AKR mouse spleen cells suppress normal AKR anti-sheep erythrocyte antibody responses in vitro. Treatment of leukemic spleen cells with DNase I prior to coculture with normal AKR cells abrogates their suppressive ability. Treatment of leukemic cells with a wide range of DNase I concentrations has no effect on the viability of these cells as measured by incorporation of [(3)H]thymidine or by eosin dye exclusion. When the activating divalent cations required for DNase I action are functionally removed in the enzyme treatment medium by chelation with EDTA, the ability of DNase I to abrogate suppression is abolished. Furthermore, the effects of DNase I in overcoming suppression are not able to be mimicked by trypsin, Pronase, or ribonuclease. These results are consistent with the existence of a population of cells in the leukemic spleen that expresses a form of membrane-associated DNA that functions in the suppression of normal antibody responses. The existence of such a population was shown by treating leukemic spleen cells with anti-single-stranded-DNA and then passing them through an anti-immunoglobulin immunoadsorption column. Approximately 15% of the leukemic cells are retained on the column and can be specifically eluted with the normal immunoglobulin. The cells of this enriched population when cocultured with normal spleen cells exhibit a 10-fold greater suppressive ability than unfractionated cells. Thus, there exists in the spleens of overtly leukemic AKR mice a population of cells expressing a form of DNA on their surfaces that in some manner is necessary for immunosuppression.