Fcreseptorer

Fcreseptorer, or Fc receptors, are a family of cell-surface receptors that bind the Fc portion of immunoglobulins. They bridge innate and adaptive immunity by translating antibody binding into cellular responses. Fc receptors are expressed on many leukocytes, including macrophages, neutrophils, NK cells, dendritic cells, mast cells, eosinophils, and subsets of B cells and platelets. They recognize the Fc region of antibodies of different isotypes, enabling distinct effector functions.

The main families are Fc gamma receptors (FcγR) for IgG, Fc epsilon receptors (FcεR) for IgE, Fc alpha receptors (FcαR) for IgA, and, less commonly, Fc mu receptors (FcμR) for IgM. FcγRs include activating receptors with ITAM signaling (e.g., FcγRI/CD64, FcγRIIA/CD32A, FcγRIIIA/CD16A) and an inhibitory receptor FcγRIIB/CD32B. The FcεRI is a high-affinity receptor on mast cells and basophils; FcαRI/CD89 is broadly expressed on myeloid cells. These receptors mediate processes such as phagocytosis, antibody-dependent cellular cytotoxicity (ADCC), degranulation, antigen presentation, and cytokine release, and they participate in immune complex clearance and regulation of B cell responses.

Genetic variation and expression levels influence binding affinity and cell-type distribution, affecting susceptibility to infections, allergic reactions, and responses to therapeutic antibodies. Clinically, Fc receptors are important in the action of antibody therapies for cancer and autoimmune diseases, and Fc engineering aims to optimize their effector functions.