Autoagglutinin produced by organ fragment cultures of mouse spleen

Mouse spleen fragment microcultures produced a heat-labile substance which agglutinated syngeneic erythrocytes. The substance reacted with an antigen present on some strains of mouse erythrocytes and on rat erythrocytes, but absent from other strains of mouse erythrocytes and from guinea pig, rabbit or sheep erythrocytes. Agglutination was inhibited by antisera to mouse immunoglobulins except for antisera specific to mouse IgM which enhanced agglutination. The agglutinin sedimented with 19 S Ig on ultracentrifugation and was destroyed by pretreatment with mercaptoethanol. Using a rosette assay increased numbers of cells, specifically binding syngeneic erythrocytes by means of a surface Ig receptor were demonstrated in spleen fragment microcultures. It is considered that the agglutinin is a noncomplement-activating IgM autoantibody and that the precursors of the cells producing the autoantibody are detected by the rosette assay.