Pertussis toxin-sensitive signal controls the trafficking of thymocytes across the corticomedullary junction in the thymus

We investigated a role of chemokines in thymocyte trafficking, Genes encodi ng stromal cell-derived factor-1 and its receptor CXCR4 were detected in th e cortex by in situ hybridization. Early immigrant cells did not express CX CR4, whereas their descendant CD44(+)CD25(+)CD4(-)CD8(-) cells did. CXCR4 e xpression was down-modulated when CD4(+)CD8(+) double-positive cells became CD4(+)CD8(-) or CD4(-)CD8(-) single-positive (SP) cells. PositiveIy select ed CD69(+)CD3(intermediate) intermediate cells gained CCR4, of which ligand , thymus activation-regulated chemokine, was expressed in the medulla, At t he next developmental stage, CD69(-)CD3(high) cells lost CCR4 but gained CC R7, These results suggest that thymocytes use different chemokines along wi th their development. Blockade of chemokine receptor-mediated signaling by pertussis toxin perturbed the normal distribution of SP cells and resulted in the accumulation of SP cells in the cortex. Thus, a pertussis toxin-sens itive event controls the trafficking of SP cells across the corticomedullar y junction.