Perinuclear antineutrophil antibody positivity Anti-myeloperoxidase antibody positivity 2021-01-23T12:16:50Z The presence of autoantibodies in the blood circulation that react against myeloperoxidase. MPO-ANCA MPO-ANCA are host-derived autoantibodies against shielded neutrophilic antigens. These antibodies react against primary granules present in neutrophils and monocytes. The formation of these antibodies has been hypothesized to be a two-step process. The first step involves exposure of neutrophils to inflammatory cytokines leading to surface exposure of cryptogenic antigens like myeloperoxidase or MPO. Next, predisposing genetic, environmental, and other factors result in the production of MPO-ANCA. In the second step, these MPO-ANCA cause damage to the host vasculature by reacting and crosslinking neutrophils to the endothelial receptors. Anti-myeloperoxidase specific antineutrophil cytoplasmic antibody Anti-MPO antibody positivity