Incompatibility associated with the bite of a brown recluse spider (Loxosceles reclusa)

Red cell samples from a patient who was suffering from massive hemolysis due to a brown recluse spider (Loxosceles reclusa) bite were found to be reactive by indirect antiglobulin test with most ABO‐compatible serum samples. Spider venom, enzymes related to those in spider venom, and antisera to plasma proteins and Rh antigens were used to investigate the unusual reactivity of the patient's cells. IgG was detected on the patient's cells by indirect antiglobulin tests. Cells treated with brown recluse spider venom or phosphatidylcholine phosphatidohydrolase reacted similarly. These findings suggest that sphingomyelinase D, which has been identified in brown recluse spider venom, may be related to the unusual reactivity of the patient's cells. Unexpected reactions were observed when venom‐treated cells were tested with Rh antibodies: O negative cells absorbed and eluted anti‐D from Rh immune globulin; E negative cells were reactive with a commercial anti‐E reagent.