The function of DPP9 (dipeptidyl peptidase 9, ENSG00000142002) is as follows. Dipeptidyl peptidase that cleaves off N-terminal dipeptides from proteins having a Pro or Ala residue at position 2 (PubMed:12662155, PubMed:16475979, PubMed:19667070, PubMed:29382749, PubMed:30291141, PubMed:33731929, PubMed:36112693). Acts as a key inhibitor of caspase-1-dependent monocyte and macrophage pyroptosis in resting cells by preventing activation of NLRP1 and CARD8 (PubMed:27820798, PubMed:29967349, PubMed:30291141, PubMed:31525884, PubMed:32796818, PubMed:36112693, PubMed:36357533). Sequesters the cleaved C-terminal part of NLRP1 and CARD8, which respectively constitute the active part of the NLRP1 and CARD8 inflammasomes, in a ternary complex, thereby preventing their oligomerization and activation (PubMed:33731929, PubMed:33731932, PubMed:34019797). The dipeptidyl peptidase activity is required to suppress NLRP1 and CARD8; however, neither NLRP1 nor CARD8 are bona fide substrates of DPP9, suggesting the existence of substrate(s) required for NLRP1 and CARD8 inhibition (PubMed:33731929). {ECO:0000269|PubMed:12662155, ECO:0000269|PubMed:16475979, ECO:0000269|PubMed:19667070, ECO:0000269|PubMed:27820798, ECO:0000269|PubMed:29382749, ECO:0000269|PubMed:29967349, ECO:0000269|PubMed:30291141, ECO:0000269|PubMed:31525884, ECO:0000269|PubMed:32796818, ECO:0000269|PubMed:33731929, ECO:0000269|PubMed:33731932, ECO:0000269|PubMed:34019797, ECO:0000269|PubMed:36112693, ECO:0000269|PubMed:36357533}.