Fc Receptor Signaling in Leukocytes: Role in Host Defense and Immune Regulation

Many leukocytes express on their surface specific receptors for immunoglobulins, termed Fc Receptors. Fc Receptors are a key component of host defense due to their ability to bind antibodies attached to infected cells or invading pathogens, thus leading to their destruction. Activation of various leukocytes through Fc Receptor stimulation results in the initiation of a plethora of cellular responses aimed at the destruction of potential pathogens. Consequently, there has been a lot of interest in elucidating the biochemical signals that Fc Receptors promote to activate these leukocyte functions. This review describes the main types of Fc Receptors, and the signal transduction pathways that are initiated by these receptors in various leukocytes. Recent discoveries on the modulation of Fc Receptor signaling by association with lipid rafts are also discussed. Emphasis is made on the signaling mechanisms governing phagocytosis, which is perhaps the best-characterized Fc Receptor-mediated cellular response. In addition, new findings on the regulatory role of Fc Receptors on immune function are also discussed.