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Systemic mononuclear-cell vasculitis in MRL/Mp-lpr/lpr mice. A histologic and immunocytochemical analysis.

The cellular mechanisms governing the expression of mononuclear cell vasculitis are poorly understood. For determination of the precise sequence of events in the development of vasculitis in autoimmune MRL/lpr mice, histologic sections from 4-20-week-old mice were evaluated with a panel of cytochemical and immunohistochemical stains. The results show that vascular disease in MRL/lpr mice develops as follows: Thy 1+, Ly 1+, L3T4- T cells assemble around predominantly small-to-medium muscular arteries at approximately 8 weeks of age. At 12 weeks of age, an adventitial inflammatory focus forms, composed of large "reactive" mononuclear inflammatory cells adjacent to hypertrophied vascular smooth muscle cells (VSMCs). Blastic Thy 1+, Ly 1+, L3T4- T cells subsequently infiltrate the tunica media, and selective VSMC karyolysis results. Occasional cytotoxic/suppressor T cells, macrophages, and possibly NK cells are noted primarily distal to the infiltration site. The outer zone of the inflammatory infiltrate is composed of mature B cells and occasional B-cell precursors. These findings suggest that cellular constituents of the immune response mediate mononuclear cell vasculitis in MRL/lpr mice.