How are autoantibodies detected?

➢ These antibodies are detected by the direct antiglobulin (Coombs) test => Direct Antiglobulin test (DAT). ➢ The patient’s RBCs are incubated with antibodies to human IgG and C3. If IgG or C3 is bound to RBCs membranes, agglutination occurs - a positive result. ➢ Direct antiglobulin test, demonstrating the presence of autoantibodies (IgG) alone, (shown here), complement alone, or both IgG + complément (C3) on the surface of the RBCs. ➢ In wAIHA, red cells coated with IgG autoantibodies (and/or complement), against a cell-surface antigen are rapidly cleared from the circulation by uptake by Fcγ receptor-bearing macrophages in the fixed mononuclear phagocytic system. ➢ Additionally, IgG antibodies also have the ability to weakly activate complement and deposit C3 fragments on RBCs, which leads to their destruction by Kupffer cells in the liver