We recently observed that specific inhibitors of postproline cleaving aminodipeptidases cause apoptosis in quiescent lymphocytes in a process independent of CD26/dipeptidyl peptidase IV. These results led to the isolation and cloning of a new protease that we have termed quiescent cell proline dipeptidase (QPP). QPP activity was purified from CD26؊ Jurkat T cells. The protein was identified by labeling with [ 3 H]diisopropylfluorophosphate and subjected to tryptic digestion and partial amino acid sequencing. The peptide sequences were used to identify expressed sequence tag clones. The cDNA of QPP contains an open reading frame of 1476 base pairs, coding for a protein of 492 amino acids. The amino acid sequence of QPP reveals similarity with prolylcarboxypeptidase. The putative active site residues serine, aspartic acid, and histidine of QPP show an ordering of the catalytic triad similar to that seen in the post-proline cleaving exopeptidases prolylcarboxypeptidase and CD26/dipeptidyl peptidase IV. The post-proline cleaving activity of QPP has an unusually broad pH range in that it is able to cleave substrate molecules at acidic pH as well as at neutral pH. QPP has also been detected in nonlymphocytic cell lines, indicating that this enzyme activity may play an important role in other tissues as well.

The typical presentation of PTB in Peruvian children includes symptoms of active pulmonary disease similar to those seen in adults. This presentation differs significantly from that reported in developed countries, where many children have minimal or no symptoms at the time of presentation. The diagnostic criteria for pediatric PTB must be modified in hyperendemic developing country environments where features may differ from those described in the United States. The triad of cough lasting >/=2 weeks, fever, and a PPD >/=10 mm was highly predictive for culture-positive PTB among children in this low-income Peruvian population.

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