The function of CST9 (cystatin 9, ENSG00000173335) is as follows. May be involved in testis development (By similarity). May play a role in hematopoietic differentiation or inflammation (PubMed:12535658). Has immunomodulatory and antimicrobial functions against Francisella tularensis, a Gram-negative bacteria (PubMed:23922243). {ECO:0000250|UniProtKB:Q9Z0H6, ECO:0000269|PubMed:12535658, ECO:0000269|PubMed:23922243}.