Critical role of Th17 cells in development of autoimmune hemolytic anemia.

Autoimmune hemolytic anemia (AIHA) is defined as the increased destruction of red blood cells (RBCs) in the presence of anti-RBC autoantibodies with or without complement activation. However, the underlying mechanism for the development of AIHA remains largely unclear. In this study, we carefully evaluated the potential role of Th17 cells in the development of AIHA. We found an elevated frequency of Th17 cells in patients with AIHA, which were closely correlated with their disease activity, including the level of anti-RBC IgG antibodies, hemoglobin, serum C3, and lactate dehydrogenase activity. Furthermore, we observed that interleukin (IL)-17 was also closely correlated with the disease activity in AIHA patients. To further elucidate the potential role of Th17 cells in induction of AIHA, we used the Marshall-Clarke and Playfair model of murine AIHA. Notably, we found that Th17 cells affected development of AIHA by enhancing the adaptive humoral responses. Specifically, we found that adoptive transfer of Th17 cells heightened the initial anti-rat RBC antibody responses and concomitantly increased the onset of AIHA. In addition, in vivo neutralization of IL-17 abrogated the development of AIHA, while initiation of anti-rat RBC IgG responses and induction of AIHA in IL-17(-/-) mice were impaired. Our findings suggest that Th17 cells contribute to the development of AIHA, which could facilitate our better understanding of AIHA pathogenesis and provide clues to developing novel forms of immunotherapy against AIHA.