Fc gamma receptors in health and disease

Receptors for the Fc fragment of immunoglobulins G (Fc gamma R) belong to t he immunoglobulin superfamily and are expressed on different cell types. Th ese receptors are classified in three different groups (Fc gamma RI, Fc gam ma RII and Fc gamma RIII) depending upon their molecular weight, affinity a nd specificity for their ligands. In addition to all these differences, gen etic polymorphisms induce the expression of several isoforms, making the Fc gamma R a heterogeneous group. The Fc gamma Rs have been the subject of in tense research on their gene organization, biochemical and structural prope rties. it has also been established that the Fc gamma R play an important f unctional role on the regulation of the biological responses that are trigg ered during inflammatory stages (e.g. an infection), as they link the cellu lar and humoral branches of the immune response. In this article we give ex amples of the participation of Fc gamma R on the regulation of the immune r esponse as well as the activation of intracellular mechanisms (transduction signals) after the crosslinking of Fc gamma R by antigen-antibody complexe s. The effect of cytokines and growth factors on the regulation of Fc gamma R expression is also described. We discuss the importance of the possible use of some of these molecules to control the expression of Fc gamma R in s ome clinical situations where alterations on their expression are associate d with some diseases. Finally, we analyze the role of Fc gamma R as the poi nt of entry of infectious agents such as HIV.