Pathogenesis of autoimmunity in αβ T cell-deficient lupus-prone mice

Murine lupus in MRL mice has been strongly attributed to alpha beta T cell-dependent mechanisms. Non-alpha beta T cell-dependent mechanisms, such as gamma delta T cells, have been shown to drive antibody and autoantibody production, but they have not been considered capable of inducing end-organ disease. Here, we have expanded upon the findings of such previous work by examining the mechanism and extent of end-organ disease attainable via gamma delta T cells and/or non-alpha beta T cell-dependent mechanisms, assessing two prototypical lupus lesions, renal and skin disease, in TCR alpha -/- MRL mice that possessed either functional or defective Fas antigen (Fas + or lpr). Observed to 1 year of age, TCR alpha -/- MRL mice developed disease characterized by increased mortality, overt renal disease and skin lesions. While delayed in onset and/or reduced in severity compared with TCR alpha +/+ MRL/lpr animals, renal and skin lesions in alpha beta T cell-deficient animals were clearly increased in severity compared with age-matched control nonautoimmune mice. In contrast to TCR alpha +/+ MRL mice, whose disease reflected pan-isotype immune complex deposition with significant complement fixation, renal disease in TCR alpha -/- MRL animals reflected predominantly IgG1 immune complex deposition, with poor complement fixation. Thus, this study demonstrates conclusively that non-alpha beta T cell-dependent mechanisms can induce renal and skin injury in murine lupus, but at least in the kidney, only via humoral autoimmunity of a relatively nonpathological isotype which results in the delayed onset of end-organ damage.