CARD9

CARD9, also known as Caspase Recruitment Domain Family, Member 9, is a protein encoded by the CARD9 gene in humans. It is a member of the CARD protein family, characterized by the presence of a caspase recruitment domain. This domain plays a crucial role in protein-protein interactions and the assembly of signaling complexes. CARD9 is primarily expressed in immune cells, particularly in myeloid cells such as macrophages and dendritic cells.

The CARD9 protein functions as a key signaling adaptor molecule within innate immune pathways. It is a critical component of the signaling cascade initiated by pattern recognition receptors (PRRs), including C-type lectin receptors (CLRs). Upon activation by microbial products or endogenous danger signals, CLRs recruit CARD9 to form multiprotein signaling complexes. These complexes then activate downstream signaling pathways, such as the NF-κB and MAPK pathways.

Through these pathways, CARD9 plays a vital role in host defense against fungal pathogens. It is essential for the proper activation of inflammatory responses and cytokine production required to clear infections. Genetic mutations in CARD9 can lead to a predisposition to invasive fungal infections, particularly those caused by Candida species and Aspergillus species, highlighting its importance in antifungal immunity. Beyond fungal infections, CARD9 has also been implicated in responses to certain bacterial pathogens and in modulating inflammatory conditions.