Human thymocytes express CCR-3 and are activated by eotaxin

Eotaxin has been characterized as a chemokine involved in eosinophil activa tion; however, mRNA for this C-C chemokine has been shown to be constitutiv ely expressed in thymus. Immunohistochemical analysis showed a punctate dis tribution pattern, with eotaxin expression localized mainly in the medulla and in Hassle's corpuscles. Moreover, the receptor for eotaxin, CCR-3, was detected on thymocytes, with the highest level of expression being on the C D8 single-positive population. Equilibrium binding analyses on unfractionat ed thymocytes demonstrated specific I-125-eotaxin binding profiles comparab le with CCR-3 transfectants. Eotaxin induced cell migration and mobilizatio n of intracellular calcium in all thymocytes except the immature CD4(-)/CD8 (-) population. Eotaxin also induced the secretion of the chemokines interl eukin-8, RANTES, and macrophage inflammatory protein-1 beta from thymocyte cultures in vitro. These results suggest that eotaxin-induced thymocyte act ivation may have important physiological implications for lymphocyte mobili zation within and from this lymphoid organ. (C) 1999 by The American Societ y of Hematology.