Macrophage inflammatory protein-1β induces migration and activation of human thymocytes

Abstract

The CC chemokine macrophage inflammatory protein 1β (MIP-1β), has been shown to be a chemoattractant preferentially activating CD4+ CD45RA+ T lymphocytes. Further analysis of chemokine action on lymphocytic cells has shown the potent migration-promoting capacity of MIP-1β on human thymocytes. The responding cells were the CD4+ and CD8+ single-positive (SP), as well as the CD4+ CD8+ double-positive (DP) populations, with little if any migratory activity on the double-negative (DN) population. The activation of thymocytes by MIP-1β appeared to be a direct, receptor-mediated event as evidenced by the rapid mobilization of intracellular calcium, increase in proteins phosphorylated on tyrosine, and activation of the mitogen-activated protein kinase (MAPK) pathway. Radioligand binding analyses showed specific and displaceable binding of MIP-1β to thymocytes with a Kd of approximately 1 nmol/L, a profile that was comparable with MIP-1β binding to CCR-5- transfected NIH 3T3 cells. In addition, CCR-5 mRNA was detected in total thymocyte populations indicating that activation of thymocytes by MIP-1β may occur through binding to CCR-5. Further dissection of the subpopulations showed that only the DP and CD8+ SP populations expressed CCR-5 and expression data on these two populations was confirmed using anti-CCR-5 monoclonal antibody. These data may be suggestive of a role for MIP-1β in human thymocyte activation, and show a potential route for HIV infectivity in the developing immune system.