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 (By similarity). 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 (PubMed:28031339). Inhibits osteogenesis by preventing osteoblast proliferation and expression of alkaline phosphatase, type I collagen, osteopontin and osteocalcin (PubMed:22792377). Acts directly as a pro-inflammatory factor in the lung through its ability to bind and activate tumor necrosis factor alpha receptor 1/TNFRSF1A (PubMed:15247912, PubMed:16709567). Interacts with host TNFRSF1A; this interaction leads to the stimulation of both surface expression and shedding of TNFRSF1A. Released from the cell wall in a glycan-free form by LytM; released early in log growth, almost no release occurs after 3 hours growth (PubMed:24434550). Anchored to the cell wall by sortase A (By similarity). Each of the immunoglobulin-binding region repeats can bind the Fc region of an immunoglobulin. Host antibody-secreting cells proliferate in the bone marrow survival niches and sustain long-term antibody titers (PubMed:28031339). In addition, osteogenesis is not inhibited and normal expression of alkaline phosphatase, type I collagen, osteopontin and osteocalcin is observed (PubMed:22792377). 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. Extended N-terminus.