CD100/Sema4D, a Lymphocyte Semaphorin Involved in the Regulation of Humoral and Cellular Immune Responses

The semaphorin family consists of soluble and membrane-bound proteins that act as chemorepulsive factors in neuronal development, thereby playing a crucial role in axon guidance. Although they are expressed in a broad range of embryonic and adult tissues, their physiological role outside the nervous system remains to be determined. Recently, emerging evidence has suggested that several semaphorins function as part of the immune system. CD100/Sema4D is the first semaphorin family member for which a critical role in the immune response has been identified. CD100 is involved in several arms of the immune response, including humoral and cell-based immunity. This review will focus on our current understanding of the role of this immunoregulatory semaphorin.