Two Distinct Categories of Warm Autoantibody Reactivity With

can be classified into two distinct categories. depending on their reactivity with reticulocyte-enriched (younger) or reticulocyte-poor (older) red cell fractions. The strength of the direct antiglobulin test (DAT) on the age-fractionated red cells of 24 patients indicated that 19 (79%) had an IgG warm autoantibody that reacted preferentially with older red blood cells. In 7 of these 19 patients (37%), the DAT was negative using reticulocyte-enriched red cell fractions. We have termed this preferential reactivity of warm autoantibodies with older red cells as type I. Five of the 24 patients studied (21 %) had an lgG warm autoantibody that demonstrated no preference for young or older red cells. U NTIL 1953, warm autoantibodies were generally considered to be “nonspecific, ” reacting with all human red cells tested. ’ However, in that year, Wiene