Chimerism occurs twice as often in lupus nephritis as in normal kidneys

Objective Systemic lupus erythematosus (SLE) is an immune‐mediated disease that particularly affects the kidneys, causing lupus nephritis. In experimental mouse models, lupus nephritis can be mimicked by inducing a chimeric state through the injection of parental T cells in offspring. In humans, pregnancy‐induced chimerism may play a role in the pathogenesis of autoimmune diseases such as SLE, but it is likely that only certain chimeric cells have pathogenic potential. In this study, we investigated whether the distribution of chimeric cells is different in the kidneys of women with SLE from that in normal kidneys, and we examined the phenotype of chimeric cells in women with SLE. Methods The presence of chimeric cells was investigated by in situ hybridization targeting the Y chromosome in 57 renal biopsy samples from 49 women with lupus nephritis. Fifty‐one kidney autopsy specimens without histomorphologic lesions served as controls. Double‐staining for the Y chromosome in combination with CD3 and CD34 markers was performed in 5 kidney specimens with lupus nephritis to identify the phenotype of the chimeric cells. Results Y chromosome–positive cells were found in 27 of 49 patients with lupus nephritis and in 13 of 51 normal controls ( P < 0.01). Both CD3+ and CD34+ chimeric cells were identified in lupus nephritis kidney specimens. Conclusion Chimeric cells are present significantly more often in kidneys with lupus nephritis than in normal kidneys, and some of these chimeric cells are T cells. This finding is interesting in light of experimental models demonstrating that lupus nephritis is initiated by chimeric T cells.