Ultrastructural study of the FVB/N mouse thymus: presence of an immature epithelial cell in the medulla and premature involution

FVB/N inbred mice have been widely used to generate a variety of transgenic lines, but their physiology and especially their immunological characteris tics are poorly documented. We therefore studied the ultrastructure of the thymus and the distribution of thymocyte subpopulations in FVB/N mice at se veral ages. In young FVB/N mice the stromal microenvironment exhibits the t hree types of epithelial cells and the two types of bone-marrow derived cel ls (macrophages and interdigitated cells) previously described in other str ains of mice. Moreover, in the thymic medulla of young FVB/N mice, a fourth cell type with the morphological characteristics of an immature epithelial cell was present in relatively high number. Furthermore, thymocyte subpopu lations distribution shows an earlier thymocyte maturation than in other st rains. Finally, changes associated with thymic involution were observed abo ut 5 months earlier than in many other mouse strains. Our results demonstra ted that the FVB/N strain has a specific immunological status. (C) 2001 Els evier Science Ltd. All rights reserved.