Adhesin that mediates binding of bacteria to a variety of host cells. Plays a role in the bacterial invasion of dentinal tubules (PubMed:9393810). A host immunostimulatory component, it modulates the innate immunity response. Plays a protective role against some antibiotics and cationic antimicrobial peptides (histatin-5, HTN3, but not beta-defensin 4A, DEFB4A) (PubMed:22609749). In the absence of the sspA gene, collagen does not induce sspB (at protein level). Single sspA deletion, bacteria invade human dental roots less well, adhere less well to collagen, decreased accumulation of mature SspB; double sspA-sspB deletion, no invasion of dental roots, collagen adherence is further reduced, as is chaining on soluble collagen (PubMed:9393810). Triple sspA-sspB-hsa deletion no longer causes human platelet aggregation; double sspA-sspB deletion still causes platelet aggregation (PubMed:19884334). Double sspA-sspB adheres better to human epithelial cells and is internalized better than wild-type cells, but induces less host cytokine production (IL-6, IL-8, monocyte chemotactic protein). Stimulates less cytokine production in mouse bone marrow-derived dendritic cells (IL-6, IL-10, IL-12, tumor necrosis factor). Increased sensitivity to antibiotics polymyxin B and nisin, and human histatin-5 (His3-(20-43)-peptide, HTN3). In intranasal mouse infection, the double mutant is cleared less quickly from lungs, neutrophil, hemokine and cytokine production are delayed or reduced (PubMed:22609749). S.gordonii, a commensal oral cavity bacteria, is among the bacteria most frequently identified as being the primary etiological agents of subacute infective endocarditis (found in 13% of cases). Belongs to the antigen I/II family.