Memory CD4+ T cells express characteristic adhesion molecules and chemokine receptors that dictate their recirculation to the tissue in which they first encountered antigen. On page 1045, Baekkevold and colleagues show that T cells may compete for access to the skin and only gain entry if they express the CC-chemokine receptor-4 (CCR4).
Previous studies showed that skin-homing and gut-homing CD4+ T cells express distinct chemokine receptors—CCR4 for skin-homing cells and CCR9 for gut-homing cells—and this was mirrored by the expression of the corresponding chemokine ligand in local blood vessels. The authors thus proposed that expression of CCR4 was required for T cells to access the skin (and CCR9 for the gut) but were perplexed by the phenotype of CCR4-deficient mice, which had normal numbers of skin-homing T cells.
Another skin-specific chemokine receptor may have compensated for the absence of CCR4. To test...
