SERUM HIGH-MOLECULAR-WEIGHT DIPEPTIDYL PEPTIDASE-IV (CD26) IS SIMILARTO A NOVEL ANTIGEN DPPT-L RELEASED FROM ACTIVATED T-CELLS

This study demonstrates that the 175-kDa form of dipeptidyl peptidase IV (DPPIV) found in normal human serum is identical with a similarly-s ized Ag, DPPT-L, found to be rapidly expressed on the surface of activ ated T cells, As activation progresses, the expression of DPPT-L reach es a peak on day 3, after which expression falls, whereas expression o f the 105-kDa CD26/DPPIV detected by the mAb 1F7 increases, as does th e ability to bind adenosine deaminase, The loss of DPPT-L from the sur face of activated T cells correlates exactly with the appearance of DP PT-L and DPPIV activity in serum-free tissue culture medium, The relea se of DPPIV was generally greater from CD4(+) cells than from CD8(+) T cells, and within the CD4(+) subset, the CD45RO(+) subset was the maj or source, which correlated with surface expression before culture, We show that the DPPIV released from activated T cells is antigenically, biochemically, and enzymatically similar to DPPIV circulating in the serum and is distinct from the DPPIV activity of 105-kDa CD26, The T c ell-released DPPIV is able to function as a costimulating molecule for the response to the recall Ag, tetanus toroid, at levels similar to t hose at which recombinant soluble CD26 and serum DPPIV exhibit costimu latory function, suggesting that the released DPPIV may serve an impor tant immunoregulatory function in vivo, both locally and within the sy stemic circulation.