CD40LG and autoimmune hemolytic anemia: Once reached a critical amount on the erythrocyte membrane aPL may activate complement leading to erythrocyte destruction; with regards to hemolysis the effect size was always greater for IgM aCL than for IgG aCL, in keeping with the fact that the IgM isotype is a powerful complement activator, to an even higher extent than the most abundant IgG1 and IgG2 isotypes, but it is not usually found on the erythrocyte surface by DAT in warm AIHA.