In situ labelling of fragmented DNA in cutaneous necrotizing vasculitis

Activation, apoptosis, and clearance of neutrophils in Wegener's granulomatosis

Wegener's granulomatosis (WG) is strongly associated with the presence of antineutrophil cytoplasmic autoantibodies (ANCAs). Within WG these ANCAs are usually (80-90%) directed against the azurophilic enzyme proteinase 3, the so called PR3-ANCA. A pathophysiological role for these autoantibodies, supported by numerous in vitro and in vivo studies, is specifically based on their capacity to bind and activate neutrophils and potentially may damage vessels. In this review, the pathogenic potential of different developmental stages of the neutrophil in the pathogenesis of WG is discussed. After release from the bone marrow into the circulation, neutrophils can be primed by TNFalpha and become attached to locally activated endothelium. Once attached to the endothelium, ANCAs can fully activate these primed neutrophils. In this activation process, the degree of activation after stimulation with PR3-ANCAs associates with the level of PR3 expression on the membrane of the neutrophil. Following activation, infiltrated neutrophils become apoptotic with further membrane expression of PR3. In WG patients, clearance of apoptotic neutrophils can be disturbed due to the opsonization of PR3-expressing apoptotic neutrophils with PR3-ANCAs, thereby perpetuating inflammation by the release of proinflammatory cytokines during clearance; or it may favor autoimmunity by PR3 presentation in an inflammatory environment. Furthermore, the presence of ANCAs and the release of the vessel-related pentraxin PTX3 may lead to the persistence of late apoptotic neutrophils in tissues, thereby inducing leukocytoclastic lesions that are characteristic in patients with WG. All together, alive neutrophils as well as apoptotic neutrophils play a key role in different inflammatory phenomena seen in patients suffering from WG.

Leukocytoclasis: ultrastructural in situ nick end labeling study in anaphylactoid purpura

In order to characterize leukocytoclasis of polymorphonuclear neutrophils (PMNs), the method of in situ nick end labeling for DNA breakdown was applied on tissue samples from 36 patients with anaphylactoid purpura at ultrastructural, as well as light microscopic, level. Light microscopic immuno-peroxidase technique showed positively labeled PMNs infiltrating in the dermis of 24 cases in which leukocytoclastic vasculitis was fully developed, suggesting that breakdown of DNA strands is triggered in the PMNs. Electron microscopic immuno-gold technique employed in six patients with the fully developed stage of inflammation identified the DNA breaks in the nuclei of PMNs. Ultrastructure of these cells, however, showed that only a minor population ( approximately 1/60) of PMNs showed the condensed and marginated nuclei, being compatible with typical apoptotic change. However, the majority of immuno-gold-labeled cells showed relatively intact nuclei without margination of condensed heterochromatin and with disintegrated cytoplasmic organelles and plasma membrane, suggesting that apoptotic cell removal mechanism may be incomplete. The immuno-gold-positive nuclear debris scattering in the tissue is most likely the remnants of unsatisfactory disposal by apoptosis of potentially injurious PMNs, resulting in the vascular and perivascular damage in leukocytoclastic vasculitis in anaphylactoid purpura.