Macrophage-like suppressor cells in rats: I. Inhibition of natural macrophage-like suppressor cells by red blood cells

The responses of rat spleen cells to T- and B-cell mitogens were inhibited following lysis of splenic red cells with either water or ammonium chloride solution. Normal responsiveness could be restored by the addition of either rat or sheep red blood cells or by the depletion of macrophages by glass adherence or carbonyl iron treatment. Conversely, the suppression of splenic mitogen responses by the addition of excess glass-adherent spleen cells could be abrogated by supplementation of cultures with red blood cells. Ammonium chloride treatment had no effect on the mitogen responses of lymph node cells. These experiments show that (i) ammonium chloride or water treatment is not toxic to any of the cells involved in responses to T- or B-cell mitogens, (ii) that normal rat spleen cells contain a population of natural suppressor cells which have the characteristics of macrophages, and (iii) that the activity of these suppressor macrophages is inhibited by red blood cells.