How is mechanism of Type III HS?

Binding of antibody to antigen and the consequent formation of antigen-antibody complexes led to the activation of classic pathway of complement system. C3b formed during complement activation coats the ICs. ↓ Erythrocytes and platelets have C3b receptors on their surface. The C3b coated ICs bind to the erythrocytes and platelets through the C3b receptors. ↓ The erythrocytes and platelets carry the ICs to the spleen and liver. The macrophages in liver and spleen, bearing Fc or complement receptors, strip the ICs on the surface of erythrocytes and platelets and phagocytose the ICs, resulting in the removal of ICs from the circulation. ➢ A healthy immune system will use macrophages in the spleen and Kupffer cells in the liver to quickly remove Immune Complexes (IC) from the bloodstream. ➢ Large complexes can be cleared by macrophages but macrophages have difficulty in the disposal of small IC.