Inhibition of oxidation activity of myeloperoxidase (MPO) by propylthiouracil (PTU) and anti-MPO antibodies from patients with PTU-induced vasculitis

Propylthiouracil (PTU) could induce antineutrophil cytoplasmic antibody (ANCA) associated vasculitis. This study aimed to investigate the inhibitory effects on MPO oxidation activity by PTU and MPO-ANCA from patients with primary microscopic polyangiitis (MPA) and PTU-induced vasculitis. IgG preparations were purified from MPO-ANCA-positive sera from seven patients with PTU-induced vasculitis and ten patients with primary MPA. The oxidation activity of MPO was measured in the presence of PTU and MPO-ANCA-positive IgG preparations from patients with PTU-induced vasculitis and primary MPA respectively. PTU could competitively inhibit the oxidation activity of MPO dose dependently. MPO-ANCA-positive IgG preparations from 6/7 patients with PTU-induced vasculitis and only 3/10 from patients with primary MPA could inhibit the MPO activity in a dose-dependent manner. In conclusions, the oxidation activity of MPO could be inhibited by PTU and PTU-induced MPO-ANCA in a dose-dependent manner, which might be involved in the pathogenesis PTU-induced vasculitis.

In vitro production of myeloperoxidase anti-neutrophil cytoplasmic antibody and establishment of Th1-type T cell lines from peripheral blood lymphocytes of patients

OBJECTIVE

To investigate the pathogenic role of T cells in the development of anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis.

METHODS

Peripheral blood lymphocytes (PBL) were isolated from myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA) associated vasculitis patients and cultured in medium. The production of MPO-ANCA in the medium of PBL stimulated with Concanavalin-A (Con-A), with or without cyclosporin (CyA), was measured by enzyme-linked immunosorbent assay (ELISA) on MPO coated plates. RNA isolated from PBMC of one patient was used for polymerase chain reaction (PCR) and single stranded conformational polymorphism (SSCP) studies, and MPO-specific T cell lines (TCL) were established by antigen stimulation techniques.

RESULTS

PBL of patients with MPO-ANCA-associated vasculitis produced MPO-ANCA following Con-A stimulation, and this effect was inhibited by treatment with cyclosporin A (CyA) or elimination of CD4 cells. PCR-SSCP showed autoantigen-reactive oligoclonal T-cell accumulation in PBMC of one of these patients. We established MPO-specific TCL which secreted interferon-gamma (IFN-gamma), but not interleukin-4 (IL-4); all TCL were CD4 positive, CD8 negative, and HLA-DR restricted.

CONCLUSIONS

Our results suggest that Th1-type T cells may mediate MPO-ANCA production, and may play a role in the onset of MPO-ANCA vasculitis.

Angiooedema due to acquired deficiency of C1-esterase inhibitor associated with leucocytoclastic vasculitis

A hereditary and an acquired type of C1-esterase inhibitor deficiency have been described. Manifestations characteristic of both forms include recurrent subcutaneous and submucosal angiooedema. Acquired C1-esterase inhibitor deficiency has been observed in association with lymphoproliferative disorders, malignancy, autoimmune diseases and infections. We report on a case with the acquired form of the disease accompanied by leucocytoclastic vasculitis. Treatment with antimalarial agents resulted in complete resolution of symptoms and signs. Furthermore, C1-esterase inhibitor concentration and activity, as well as C1 levels, all returned to normal.

Factor XIIIa+ dermal dendrocytes in erythema elevatum diutinum and ordinary cutaneous leukocytoclastic vasculitis lesions

Factor XIIIa+ dermal dendrocytes belong to the dermal microvascular unit and are related to wound healing, angiogenic and fibrogenic processes. Erythema elevatum diutinum (EED) is a leukocytoclastic vasculitis followed by repair and fibrosis. In order to verify the involvement of fXIIIa+DD in the pathogenesis of EED and ordinary leukocytoclastic vasculitis (OLV) these cells were immune labeled with anti-factor XIIIa antibody and quantified in 15 biopsies of EED, 18 of OLV and compared with 11 fragments of normal skin (NS). The number of vessels was evaluated by endothelial cell staining with anti CD34 antibody. FXIIIa+DD appeared in both groups of vasculitis with hyperthophic dendrites, with no difference in their number at any level of the dermis. The number of fXIIIa+DD in the superficial dermis was higher in OLV than in NS (p<0.001). The number of dermal vessels in the EED group was higher at all dermis depths evaluated when compared with NS (p<0.05) and in the middle and deep dermis when compared with OLV (p<0.05). The results suggest the participation of fXIIIa+DD in the immunopathological mechanisms of both groups of vasculitis studied. However, there was no correlation between the number of fXIIIa+DD and angiogenesis and fibrogenesis in the EED lesions.

Early vasculitis in the mercuric chloride induced Brown Norway rat model is neutrophil independent

In the Brown Norway rat, mercuric chloride (HgCl2) induces an autoimmune syndrome characterized by necrotizing vasculitis, predominantly affecting the caecum, and a polyclonal B-cell response. The time course of vasculitis is biphasic, with an alphabeta T-cell independent phase occurring within 24 h, and a T-cell and neutrophil dependent phase, maximal at two weeks. The pathogenesis of the early phase of vasculitis is unclear, and this study aims to examine the role of neutrophils. Rat neutrophils were depleted using cyclophosphamide. RP3, an antirat neutrophil monoclonal antibody, inhibited neutrophil leucocytosis but did not deplete neutrophils. Vasculitis was induced by subcutaneous HgCl2 injection. Serial measurements of peripheral blood leucocyte count were made. Rats were killed after 24 or 72 h. The macroscopic appearance of the caecum was scored by an experienced observer, and samples taken for histological examination. Caecums were excised and myeloperoxidase, a marker enzyme for neutrophil infiltration, assayed. Cyclophosphamide induced marked neutropaenia whereas RP3 inhibited the neutrophilia observed after HgCl2 injection. Vasculitis was present in both treated and control animals, with no significant differences in macroscopic or microscopic scores between the groups. Tissue myeloperoxidase activity was low in all animals and did not differ significantly between groups. The data do not support a role for neutrophils in the initial pathogenesis of vasculitis in this model.

Protective effects of inhibitors of nitric oxide synthase in immune complex-induced vasculitis

1. The ability of analogues of L-arginine (N-iminoethyl-L-ornithine (L-NIO), NG-monomethyl-L-arginine (L-NMMA), NG-nitro-L-arginine methyl ester (L-NAME) and NG-nitro-L-arginine (L-NNA)) to protect against inflammatory injury induced by activated neutrophils was investigated in rats following intradermal or intrapulmonary deposition of immune complexes. 2. The descending order of potency for protective effects of these analogues was: L-NIO > L-NMMA > L-NNA = L-NAME. The approximate IC50 value for L-NIO in the dermal vasculitis model was 65 microM. For all other compounds, the IC50 values were > 5 mM. 3. The protective effect of L-NIO in the skin was reversed in a dose-dependent manner by the presence of L-arginine, but not by D-arginine. L-Arginine also reversed the protective effects of L-NIO in immune complex-induced lung injury. 4. The protective effects of L-NIO were not associated with reductions in neutrophil accumulation, as measured by extraction from tissues of myeloperoxidase. 5. These data demonstrate that L-NIO has the most potent protective effects against immune complex-induced vascular injury induced by activated macrophages. Furthermore, they indicate that this injury is dependent upon the generation of nitric oxide.