Mouse Langerhans cells differentially express an activated T cell-attracting CC chemokine

Epidermal Langerhans cells represent an immature population of dendritic ce lls, not yet able to prime naive T cells. Following in vitro culture Langer hans cells mature into potent immunostimulatory cells. We constructed a rep resentative cDNA library of in vitro matured murine Langerhans cells. Apply ing a differential screening procedure 112 differentially expressed cDNA cl ones were isolated. Thirty-six clones represented cDNA fragments of the sam e gene, identifying it to be the most actively expressed gene induced in ma turing Langerhans cells. A full-length cDNA was sequenced completely. The o pen reading frame codes for a protein of 92 amino acids containing a leader peptide of 24 amino acids, yielding a mature protein of 7.8 kDa molecular weight. Database searches revealed 99.4% sequence identity on the nucleotid e level to the recently described mouse CC chemokine ABCD-1, as well as 74% sequence identity to the human CC chemokine, the macrophage-derived chemok ine/stimulated T cell chemotactic protein. Expression was analyzed by rever se transcriptase-polymerase chain reaction on a large panel of cell types. Unlike the macrophage-derived chemokine, expression was not detected in mac rophages stimulated by various cytokines, Expression is restricted to cultu red Langerhans cells, in vitro cultured dendritic cells, and lipopolysaccha ride-activated B cells. Recombinant protein was expressed in the yeast Pich ia pastoris and purified to homogeneity. Whereas no chemotactic activity wa s observed in chemotaxis assays for naive T cells, B cells, cultured dendri tic cells, and Langerhans cells, a strong chemoattractant activity was exer ted on activated T cells. Thus, production of this chemokine by dendritic c ells may be essential for the establishment and amplification of T cell res ponses.