Relationship between Structure and Function of Lower Vertebrate Immunoglobulins

Abstract

In order to elucidate both macromolecular and genetic bases for the functional diversity expressed by immunoglobulins, extensive studies of their primary, secondary, tertiary and quaternary structure have been undertaken (1–3). Early in the course of these investigations, it became apparent that antibody function was associated with a heterogeneous group of multimeric glycoproteins and that more than one gene controlled the synthesis of individual immunoglobulin subunits. The mechanism whereby the separate gene products are generated (somatic mutation or germ line accumulation) and ultimately integrated are not fully understood (4, 5). As biologic processes such as antibody formation may have become more complex during the passage of evolutionary time, one major direction in the investigation of adaptive humoral immunity has been to evaluate the immune response and antibody structure in phylogenetic perspective. Although the characterization of lower vertebrate immunoglobulins is not as complete as that of the mammalian counterparts, sufficient detail of their structure is known to permit meaningful phylogenetic comparisons. This presentation will first outline the central structural features of mammalian IgM and IgG, compare the structures of lower and higher vertebrate forms of immunoglobulins, relate immunoglobulin structure to active site formation and expression and discuss the origins of non-immunoglobulin mediated “immune-like” recognition in invertebrate and vertebrate species.