Hemoglobin alpha regulates T-lymphocyte activation and mitochondrial function.

Hemoglobinopathies affect approximately 7% of the global population and are associated with an increased risk of autoimmune disorders, though the underlying mechanisms remain unclear. Hemoglobin is traditionally recognized for its role in oxygen transport within erythrocytes, but its expression in other cell types has been documented. We have recently discovered hemoglobin alpha a1 (Hbα-a1 mRNA and Hbα protein) in T-lymphocytes and previously reported that its expression was sensitive to mitochondrial redox perturbations. However, outside of its incidence and basic characterization, the functional role of Hbα in T-lymphocytes remained unknown. Herein, we identify Hbα in both CD4(+) and CD8(+) T-lymphocyte subsets, and found its expression is highly dynamic, differs between the two subtypes, and is dependent upon activation stage. Further, the loss of Hbα impairs mitochondrial function, dysregulates cytokine production, and lowers the activation threshold primarily in CD4(+) T-lymphocytes, indicating a critical role for Hbα within this subset. While these data suggested the loss of Hbα in T-lymphocytes may promote aberrant activation of autoreactive T-lymphocytes, surprisingly, we discovered that mice lacking Hbα in T-lymphocytes exhibited reduced severity of experimental autoimmune encephalomyelitis (EAE) compared to wild-type control animals. Interestingly, T-lymphocytes lacking Hbα in vivo appeared to function identically to wild-type controls, which did not explain the protection against EAE. In contrast, T-lymphocyte Hbα knock-out mice displayed significantly reduced levels of circulating immunoglobulins and CD40L expression compared to their wild-type counterparts during EAE, suggesting impaired intercellular communication. These data elucidate a previously unrecognized role for Hbα in T-lymphocyte function with implications for hemoglobinopathies.