Cellular steps in the pathogenesis of cutaneous necrotizing vasculitis.

Abstract

Cutaneous necrotizing vasculitis (CNV) have been traditionally divided into "leukocytoclastic" and "lymphomonocytic" forms. The etiology and the pathogenesis of the two forms are not clear. We studied by immunohistochemistry and electronmicroscopy the infiltrate of 5 cases of leukocytoclastic form and 5 cases of lymphomonocytic form of CNV in two phases (early and late). Aim of the study was to evaluate: 1. the immunophenotypical characteristics of the infiltrate; 2. the expression of some adhesion molecules receptors; 3. the ultrastructural characteristic of the infiltrate; 4. the possible sequence of the events. Our results showed, by immunohistochemistry, a rich infiltrate of CD3+, CD4+, CD1a+ cells in both phases of lympho-monocytic vasculitis and a poor infiltrate of CD4+, CD1a+ and CD36+ cells in the early phase of leukocytoclastic vasculitis, while the perivascular infiltrate was rich of these cells in the late phase of this latter form. ICAM-1 and LFA-1 were strongly expressed in lympho-monocytic vasculitis. By electronmicroscopy, most infiltrating cells showing the ultrastructural markers of immature cells of dendritic lineage were in contact with each other and with lymphocytes and perivascular dendritic macrophages in lymphocytic form and in the late phase of leukocytoclastic form. Our results suggest that lymphocytic vasculitis might be related to a cell-mediated immune reaction and that the leukocytoclastic form of CNV, formerly considered a typical neutrophilic disease, is also maintained by a cell-mediated immune response to not yet identified endogenous antigens released in the lesional area.