May be involved in testis development (PubMed:9826679). May play a role in hematopoietic differentiation or inflammation (By similarity). Has immunomodulatory and antimicrobial functions against Francisella tularensis, a Gram-negative bacteria (PubMed:23922243). Expression is restricted to fetal gonads and adult testis. Expressed during testis cord formation in pre-Sertoli cells, at a time immediately after the peak of SRY expression. No visible phenotype; probably due to redundancy with other family members. Belongs to the cystatin family.