Abstract
BACKGROUND: Failure of humoral tolerance to red blood cell (RBC) antigens may lead to autoimmune hemolytic anemia (AIHA), a severe and sometimes fatal disease. Previous studies have shown that although tolerance is robust in HOD mice, autoantibodies are generated upon adoptive transfer of OTII CD4(+) T cells, which are specific for an epitope contained within the HOD antigen. These data imply that antigen-presenting cells (APCs) are presenting RBC-derived autoantigen(s) and are capable of driving T-cell activation. Given that multiple APCs participate in erythrophagocytosis, we used a transgenic approach to determine which cellular subsets were required for autoantigen presentation and subsequent autoreactive T-cell activation. STUDY DESIGN AND METHODS: HOD mice, which express an RBC-specific antigen consisting of hen egg lysozyme, ovalbumin, and human blood group molecule Duffy, were bred with IAb(fl/fl) and Cre-expressing transgenic animals to generate mice that lack I-A(b) expression on particular cell subsets. OTII CD4(+) T cell proliferation was assessed in vivo in HOD(+) I-Ab(fl/fl) xCre(+) mice and in vitro upon coculture with sorted APCs. RESULTS: Analysis of HOD(+) I-Ab(fl/fl) xCre(+) mice demonstrated that splenic conventional dendritic cells (DCs), but not macrophages or monocytes, were required for autoantigen presentation to OTII CD4(+) T cells. Subsequent in vitro coculture experiments revealed that both CD8(+) and CD8(-) DC subsets participate in erythrophagocytosis, present RBC-derived autoantigen and stimulate autoreactive T-cell proliferation. CONCLUSION: These data suggest that if erythrocyte T-cell tolerance fails, DCs are capable of initiating autoimmune responses. As such, targeting DCs may be a fruitful strategy for AIHA therapies.