Caspase recruitment domain-containing protein 9 is an adaptor protein of the CARD-CC protein family, which in humans is encoded by the CARD9 gene. It mediates signals from pattern recognition receptors to activate pro-inflammatory and anti-inflammatory cytokines, regulating inflammation. Homozygous mutations in CARD9 are associated with defective innate immunity against yeasts, like Candida and dermatophytes. CARD9 is a member of the CARD protein family, which is defined by the presence of a characteristic caspase-associated recruitment domain (CARD). This protein was identified by its selective association with the CARD domain of BCL10, a positive regulator and NF-κB activation. It is thought to function as a molecular scaffold for the assembly of a BCL10 signaling complex that activates NF-κB. Several alternatively spliced transcript variants have been observed, but their full-length nature is not clearly defined.