INTERLEUKIN-7 INFLUENCES THE DEVELOPMENT OF THYMIC DENDRITIC CELLS

Interleukin-7 (IL-7) has been shown to be a critical factor in B and T lymphopoiesis, and to influence the differentiation of myeloid cell l ineages. In the present study we extend these results demonstrating th at IL-7 also plays an important role in the development of thymic dend ritic cells (DC). The addition of IL-7 to rat fetal thymus organ cultu res (FTOC) resulted in a drastic increase in the number of CD3(-)CD4(- )CD8(-) cells, which mostly expressed typical DC markers, including ma jor histocompatibility complex class II, OX-62, CD11b, CD68, and CD54. These cells exhibited morphological and ultrastructural features of D C, and were potent stimulators of the allogeneic mixed leukocyte react ion. Although increased numbers of DC were continuously generated thro ughout the culture period in the presence of IL-7, they were not activ ely dividing, indicating that DC in IL-7-treated cultures did not aris e by expansion of pre-existing cells. Reduced DC numbers obtained afte r the addition of neutralizing anti-IL-7 antibodies to mouse FTOC conf irmed the relevance of endogenously produced IL-7 on thymic DC develop ment. Furthermore, the addition of IL-7 to FTOC derived from severe co mbined immunodeficient mice also generated large numbers of DC in the absence of thymocyte maturation. (C) 1998 by The American Society of H ematology.