Relation of reticulocytosis to positive Coombs tests in NZB and other mice.

S EVERAL RECENT REPORTS have incriminated reticulocytes as the cause of “false positive” Coombs tests obtained in spontaneous or experimentally induced anemia.14 As reticulocytosis is frequently associated with the spontaneous Coombs positive hemolytic anemia which develops in NZB mice, and because the positive Coombs test has been used by Holmes and Burnet5T as the main basis for calling the condition autoimmune, it seemed important to establish whether or not a possible pseudoreaction caused by reticulocytes was contributing to the test. Two general approaches were used. First, the temporal relationship between reticulocytosis and positive Coombs tests in NZB was examined. Second, four rabbit antisera with well-defined specificities were used as Coombs test reagents and for immunoelectrophoresis to study phenylhydrazine-induced reticulocytosis in NZB, C3H, C57/B1, and Hall Instiute mice, with the aim of characterizing any cell coatings giving rise to a positive Coombs test. The results indicate that reticulocytosis does not contribute to the positive Coombs tests reported for NZB mice, and that “false positive” Coombs tests are caused by reticulocytes only when antisera of broad specificity are used.