Diverse Roles of Semaphorins on T Cell Activation, Differentiation, Migration, and Effector Functions.

Semaphorins are a large family of proteins originally identified for their roles in axon guidance during neural development. Recent findings have established the importance of semaphorins members in modulating diverse immune responses of T cells in vitro and in vivo. Class 3 semaphorins, typified by Sema3A, signal through Neuropilin-1 and Plexin-A receptors in an activation-dependent manner, suppressing effector proliferation while promoting regulatory T cell stability and shaping cytokine profiles in autoimmunity and cancer. Sema3E and Sema3F similarly fine-tune host defense and inflammation by directing Th1/Th17 responses or restraining aberrant chemotaxis. Class 4 members, such as Sema4A and Sema4D, engage Plexin-B1, Plexin-D1, and CD72 to deliver both "forward" co-stimulatory and "reverse" signals: they amplify CD4+ and CD8+ effector functions, support T helper-B cell crosstalk, and influence tumor immunity via receptor shedding and bidirectional signaling. Finally, although less well defined, class 7 Sema7A operates indirectly-through APCs and Tregs-to regulate inflammatory recall responses and Th1/Th17 driven pathology. Together, these semaphorin-mediated pathways underscore a complex, context-dependent network that balances protective immunity against immunopathology, offering novel therapeutic targets in autoimmunity, infection, and cancer.