CD1a molecules traffic through the early recycling endosomal pathway in human Langerhans cells

In this work, we studied the localization and traffic of CD1a molecules in human epidermal Langerhans cells and the ability of these cells to stimulat e CD1a-restricted T cell clones. We found that CD1a was spontaneously inter nalized into freshly isolated Langerhans cells, where it was rapidly distri buted to the early/sorting endosomes and then to the early/recycling endoso mes. In the latter compartments, CD1a colocalized with Rab11, a small GTPas e known to be involved in the recycling of transmembrane proteins from earl y endosomes to the cell surface. In the steady state, intracellular CD1a wa s mainly located in Rab11(+) recycling endosomal compartments. When endocyt osis was blocked, intracellular CD1a moved rapidly from the early/recycling endosomes to the cell surface where it accumulated. The resultant increase in the cell surface expression of CD1a enhanced the capacity of Langerhans cells to stimulate a CD1a-restricted T cell clone. These findings are cons istent with a dynamic exchange of CD1a between recycling compartments and t he plasma membrane and suggest that the antigen-presenting function of CD1a depends on its traffic through the early/recycling endosomal pathway.