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 im-munization of mice with the human B-lineage acute lymph-oblastic leukemia cell line Pre-ALP. Under reducing condi-tions, 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 hor-mones. Using M27 antibody, CPM was detected only at dis-crete B lymphocyte developmental stages, namely on com-mitted 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-P EPTIDE HORMONES, produced by multiple tissues, play an important role in the regulation of immune response^." ^ The activity of most peptide hormones is locall