Semaphorin 4A is dynamically regulated during thymocyte development in mice.

Semaphorins are important regulators of peripheral T and B-cell mediated immune responses in mice and humans. Modulatory roles of semaphorins in T cell development are also being characterized. We carefully analyzed the gene expression and protein levels of semaphorins 4A, 4D, and 7A at various developmental stages of T cell maturation in the thymus of C57BL/6 mice. Sema7a was expressed at very low levels, while Sema4d was abundant at all developmental stages of mouse thymocytes. We found the most interesting pattern of gene regulation and protein localization for semaphorin 4A. Both semaphorin 4A mRNA and protein were clearly detected on the earliest progenitors and were downregulated through thymic development. SEMA4A protein also showed a distinct cortico-medullary pattern of localization. Our findings contribute to an understanding of the complex roles played by semaphorins in the network of spatially and temporally regulated cues underpinning T cell development in the thymus.