Structure and function of immunoglobulins

Abstract

Efficient elimination of pathogens from the host's body needs the cooperation of recognition/receptor molecules of adaptive and innate immunity. Receptors of innate immunity are germline gene encoded and fixed to recognize a limited number of structures only. Structures on pathogens however are very diverse and they can undergo changes due to selection pressure. Some recognition proteins of adaptive immunity, i.e. immunoglobulin molecules, can be recognized as biochemical transducers which reduce the diversity of antigenic epitopes of microbes to a few principal structures. These principal structures are such that recognition/receptor molecules of innate immunity can cope with: complement can be activated efficiently and receptors of the reticuloendothelial system (RES) can ensure ultimate elimination of pathogens, their debris and their metabolic products. The structure of immunoglobulins perfectly fits their transducer function: the bipolar molecules have variable regions for recognition of diversity of antigenic epitopes and have a few different constant regions which mediate effector functions. The first part of this review focuses on the transducer function of high-affinity, narrowly tuned in host defense and in elimination of senescent and altered self by low-affinity cross-reactive immunoglobulins. In a second part the review gives an outlook on how recognition by immunoglobulins of host's structures may help to attenuate overshooting inflammation (cytokines, complement) and tissue destruction by inappropriate complement activation. Finally immunoglobulin preparations, which have been used in clinic, will be mentioned briefly. These have helped considerably to understand immunoglobulin function in humans.