Anti‐i, a Frequent Cold Agglutinin in Infectious Mononucleosis

Anti-I and anti-i display preferential cold agglutination of red cells from normal adults and cord bloods respectively. Weak agglutinability by anti-I of red cells from some adults has been described [12] and genetic control for these differences has been postulated [6, 111. Using both kinds of test sera, erythrocytes from normal adults are I-positive and i-weak (or i-negative) whereas red cells from cord blood and from adults with unusual Ii genotype are i-positive and I weak (or I-negative) [6, 8, 111. In certain erythropoietic disorders increased i agglutinability has been observed [4], whereas partial loss of I agglutinability has been described in leukemia [lo]. The sera of genetically determined I-negative, i-positive adults often contain agglutinating and lytic anti-I [6, 111. Complement fixation and immune hemolysis may be mediated by anti-I and anti-i, and may be associated with acquired hemolytic anemia (AHA) [5, 71. In the present investigation cold agglutinins having anti-i specificity were demonstrated in a very high proportion of native sera obtained from patients having infectious mononucleosis (IM). Two independent lines of investigation led to this study. At The Mount Sinai Hospital a patient presented with a combination of I M and AHA, and was found to have both heterophile and anti-i serum agglutinins. The details of this case will be described separately [Z]. Studies of in vitro modification in the expression of erythrocytic I and i antigens [lo] led to examination of IM sera a t the National Institutes of Health.