Semaphorin 3a - A New Intrathymic Suppressor Factor

Abstract

Semaphorins were originally identified as axon guidance factors involved in the development of the neuronal system. However, accumulating evidence indicates that several semaphorins, so-called ‘immune semaphorins’, are also involved in various phases of immune responses. One of such factors is semaphorin 3A - a member of class 3 semaphorins, which are secretory molecules in vertebrates. There are multiple mechanisms involved in the process of semaphorin 3A-mediated regulation. One of them is down-regulation of peripheral T-cell activity in consequence of which semaphorin 3A is considered as an immunosuppressive factor. But semaphorin 3A is also expressed in the thymus while its function there remains obscure. Here are discussed new data on immunosuppressive function of this factor towards thymocytes and thymic epithelial cells, obtained in vitro. Because it is involved both in physiological immunoregulation and in the pathogenesis of many autoimmune, atopic, and malignant diseases, semaphorin 3A turns to be a promising therapeutic tool to be studied and applied in these diseases.