Plays a role in the inhibition of the host innate and adaptive immune responses. Possesses five immunoglobulin-binding domains that capture both the fragment crystallizable region (Fc region) and the Fab region (part of Ig that identifies antigen) of immunoglobulins (PubMed:2938951, PubMed:4163007, PubMed:10805799). In turn, Staphylococcus aureus is protected from phagocytic killing via inhibition of Ig Fc region. In addition, the host elicited B-cell response is prevented due to a decrease of antibody-secreting cell proliferation that enter the bone marrow, thereby decreasing long-term antibody production. Inhibits osteogenesis by preventing osteoblast proliferation and expression of alkaline phosphatase, type I collagen, osteopontin and osteocalcin. Acts directly as a pro-inflammatory factor in the lung through its ability to bind and activate tumor necrosis factor alpha receptor 1/TNFRSF1A (By similarity). Interacts with host TNFRSF1A; this interaction leads to the stimulation of both surface expression and shedding of TNFRSF1A. Cell wall anchoring is confered by the LPXTG motif and following sequences (PubMed:1638631). Anchored by sortase A (PubMed:10427003). SpA from strains A676 and V-I is secreted whereas SpA from Cowan 1 and 8325-4 is mostly attached to the cell wall (Probable). Newly synthesized protein is deposited at 2-4 foci/cell and eventually is distributed in a ring around the cell (PubMed:17416657). More protein is secreted in a secG or double secG/secY2 mutant (at protein level). Each of the immunoglobulin-binding region repeats can bind the Fc region of an immunoglobulin (PubMed:2938951). Cell wall anchoring is confered by the LPXTG motif and following sequences (residues 482-516) which are necessary and sufficient to target other proteins to the cell wall (PubMed:1638631). The YSIRK-G/S motif in the signal sequence plays a role in the secretion efficiency for SpA, it may have a specialized recognition mode (Probable). Decreased virulence in mice (PubMed:3679545). Bacteria do not bind IgG (PubMed:12700270). No visible phenotype during growth in liquid culture (PubMed:22447609). Important immunodiagnostic reagent because of its ability to bind the Fab and Fc fragments of a wide range of mammalian immunoglobulins. Belongs to the immunoglobulin-binding protein SpA family.