Tissue chimerism in systemic lupus erythematosus is related to injury

Background: Chimerism indicates the presence of cells from one individual in another individual, and has been associated with several autoimmune diseases. Although this finding may point towards a role for chimerism in the induction of SLE, it could also indicate that chimerism is the result of repair mechanisms after injury. Objective: To perform a post-mortem investigation for the presence of chimerism in 48 organs from seven women with SLE and establish whether there was a relationship between chimerism and injury. Methods: Chimeric male cells in female tissue specimens were identified by in situ hybridisation of the Y-chromosome. Organs were categorised into four different groups according to injury experienced. Results were compared with those for unaffected control organs. Results: Chimerism was found in all seven patients with SLE. Y-chromosome-positive cells were present in 24 of 48 organs from women with SLE, which was significantly more than in control organs (p<0.001). Chimerism occurred more often in organs from patients with SLE who had experienced injury than in normal control organs, irrespective of whether the injury experienced was SLE-related, non-SLE-related or both. Conclusions: This is the first report of the distribution of chimerism in a large number of organs from women with SLE. It shows that the occurrence of chimerism is related to injury. The data support the hypothesis that tissue chimerism is the result of a repair process.