Autoantibodies to myeloperoxidase (MPO) are associated with small vessel systemic vasculitis. Interactions of these autoantibodies with MPO target antigen, Fcgamma receptors and Beta2 integrins at the neutrophil surface, can set in train a sequence of intracellular signal transduction events that culminate with functional responses. These include a respiratory burst with release of superoxide ions, degranulation, cytokine release, enhanced adhesion and induction of an accelerated apoptotic program.