CD26 is expressed on a restricted subpopulation of dendritic cells in vivo.

Two major sub-populations of dendritic cells (DC) are present in afferent lymph draining the skin of cattle distinguished by expression of signal regulator protein alpha (SIRPalpha). The SIRPalpha(-) population expresses the uncharacterized bovine WC10 antigen (Ag). Initial N-terminal sequencing of the WC10 protein purified by affinity chromatography showed significant homology with human CD26. A cDNA encoding bovine CD26 was cloned and the recombinant molecule expressed in COS-7 cells. Transfectants abrogated the ability of macrophage-derived chemokine (MDC) to cause a calcium flux in bovine PBMC indicating enzymatic activity characteristic of CD26. They also stained with WC10 monoclonal antibody confirming that the Ag is CD26. This is the first description of CD26 expression by DC in vivo or in vitro. It is expressed on a sub-population of ex vivo DC in afferent lymph draining the skin and on sub-populations of DC isolated from prescapular and mesenteric lymph nodes draining the skin or intestine, respectively. CD26 is an exopeptidase with specificity for motifs within the receptor-binding domain of several chemokines including MDC. CD26 mediated truncation of MDC affects the Th cell response effected by the chemokine and may produce a Th1 bias. Transcripts for MDC were present in both CD26(+) and CD26(-) DC, thus CD26 mediated modification of MDC may bias the immune response induced in naive T cells by DC.