Mechanisms of erythrocyte destruction: Comparison of canine immune-mediated hemolytic anemia and normal senescent destruction

Normal senescent destruction of red blood cells (RBCs) is an age-dependent process. Cells of many mammalian species circulate for a finite period of time and then rapidly removed by macrophages of the mononuclear phagocyte system. The most widely accepted hypothesis for senescence destruction is one in which immunologic mechanisms participate. Alteration of the erythrocyte membrane may elicit binding of self-reacting IgG antibodies with subsequent removal by macrophages. Understanding senescent destruction of RBCs may aid in understanding pathologic destruction of erythrocytes associated with immune-mediated hemolytic anemia.;In vitro aging of RBCs from healthy dogs was studied using density gradient separation techniques to determine if storage produced changes similar to those that occur during senescence in vivo. In vitro storage of canine RBCs was associated with increased cell density, hemoglobin content, IgG binding, and glycosylated hemoglobin concentrations, however, under the conditions used in this study, the highest concentrations of IgG and HbA1 did not correlate with the most dense cells. These data question the use of density gradient centrifugation as a means of isolating senescent canine RBCs.;A retrospective study of canine immune-hemolytic anemia (IMHA) was performed to characterize clinical, hematological and immunological data in dogs with naturally occurring IMHA and to investigate possible prognostic indicators. Immunoglobulin pattern and bilirubin concentrations were useful prognostic indicators whereas the severity of anemia at admission and absence of regeneration were not. The sensitivity of the direct antiglobulin (Coombs') test was compared to that of an indirect flow cytometric assay (FCA) for the detection of antierythrocyte IgG in dogs with primary or secondary IMHA. Sensitivities of both test were comparable, however, each failed to detect approximately 20% of IMHA cases.;Erythrocyte antigen binding sites of normal dogs and dogs with autoimmune hemolytic anemia (AIHA) were studied using immunoblotting. Two previously unreported canine erythrocyte membrane proteins (88 kD, 80 kD) specific to AIHA-positive patients were identified. These proteins are likely clinically significant. A nonspecific membrane protein (over 200 kD) that bound to sera of both normal dogs and dogs with AIHA was identified. We suggest that this protein may be involved in the normal clearance of senescent or damaged erythrocytes.