Staphylococcus aureus secretes a diverse arsenal of virulence factors that interfere with the host immune response and contribute to the pathogenesis of infection. The staphylococcal superantigen-like (SSL) family is one such family of virulence factors. Originally identified by their sequence homology to superantigens none of the SSL proteins described have any superantigen activity. Instead the SSL proteins appear to interact with various aspects of innate immunity such as inhibition of inflammatory cell recruitment and complement inhibition. There are 14 known members of the SSL family located in two clusters, the first cluster containing ssl1-11 is located on the vSaα genomic island and the second cluster containing ssl12-ssl14 is located on the vSaγ genomic island. SSL14 is a member of this family with no known function. Identification of proteins that bind immobilised SSL14 include fibronectin, fibrinogen and the complement component C1q from human sera. C1q is part of the C1 complex, which is the first component of the classical pathway. The C1 complex binds to antibodies bound to foreign molecules and initiates the classical complement cascade. SSL14 is able to inhibit the classical pathway in a concentration-dependent manner and the residues involved are located in the C-terminal domain of SSL14.