Failure of cytotoxic agents to inhibit the clearance of sensitized erythrocytes

The effects of cytotoxic agents on the clearance of erythrocytes sensitized with Ab and/or complement were studied. A known quantity of highly purified, high avidity, rabbit IgG or IgM anti guinea pig erythrocyte Abs was used to sensitize ⁵¹Cr labeled erythrocytes. These labeled, Ab coated red cells were injected into guinea pigs treated with azathioprine or cyclophosphamide and into controls. Cell survival and sites of sequestration were determined. Azathioprine and cyclophosphamide did not inhibit the hepatic clearance of IgM sensitized erythrocytes or the splenic clearance of IgG coated erythrocytes. At low levels of IgG sensitization, cyclophosphamide in fat increased the magnitude of clearance. In this case, the hypoplastic bone marrow was responsible for the increased sequestration. Previous studies in normal, corticosteroid treated and chronically infected guinea pigs have never shown bone marrow sequestration. This study demonstrates that cytotoxic agents do not impair the clearance of sensitized red cells, but in certain circumstances may augment or alter the site of clearance. (25 references)