Distribution of carboxypeptidase M on lymphoid and myeloid cells parallels the other zinc-dependent proteases CD10 and CD13.

Monoclonal antibody (MoAb) M27 was generated after immunization of mice with the human B-lineage acute lymphoblastic leukemia cell line Pre-ALP. Under reducing conditions, MoAb M27 precipitated a 60-kD surface-membrane molecule from Pre-ALP cells. Expression cloning of Pre-ALP cDNA showed that M27 recognizes carboxypeptidase M (CPM), a cell-surface, zinc-dependent protease known to cleave off basic C-terminal amino acids from peptide hormones. Using M27 antibody, CPM was detected only at discrete B lymphocyte developmental stages, namely on committed precursors and on germinal center cells. CPM was also expressed on mature T cells, mainly after activation. These results provide the first description of a carboxy-peptidase on lymphoid cells. In addition, CPM was found on granulocytes and monocytes, but not on their progenitors. Strikingly, CPM was present only on CD38+ cells, irrespective of lineage affiliation. Of interest, CPM displayed a largely overlapping distribution with the CD10 and CD13 peptidases, with which it shares common substrates (enkephalins, bradykinin). Collectively, the present data show a previously unrecognized distribution pattern of CPM on lymphoid and myeloid cells and suggest that CPM may cooperate with CD10 and CD13 to regulate biologic activity of peptide hormones on leukocytes.