It is well established that the mast cell is the primary effector cell in urticaria, but the mechanism of its skin-specific activation should be elucidated to understand the pathogenesis of urticaria. Cutaneous mast cells, but not those from other sites, are selectively activated by C5a and substance P (SP). We observed the spontaneous release of SP in skin chambers attached on skin of patients with severe chronic urticaria.
In vitro stimulation of skin slices with SP revealed heterogeneity among the skin donors. Some released LTB
4, TNFα, and histamine; Others released LTB
4 or TNFα and histamine or histamine alone. Such heterogeneity may account for the cell infiltration observed in some cases of chronic urticaria. Recent work has revealed that about one third of patients with urticaria have circulating histamine-releasing autoantibodies against the high affinity IgE receptor (FcεRI) and, less commonly, against IgE (“autoimmune urticaria”). HLA analysis has suggested the presence of a genetic diathesis for this subgroup of urticaria, but neither clinical nor histopathological investigations distinguished this subgroup from the other. Cysteinyl leukotriene receptor antagonists, such as montelukast and zafirlukast, have been reported to be effective for treating patients that did not respond to histamine receptor antagonists, but others have reported no effect with these drugs. For patients with autoimmune urticaria, the effectiveness of immunosuppressive therapies, such as cyclosporin, intravenous immunoglobulin, and plasmapherasis, have been reported in parallel with the reduction of circulating autoantibodies.
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