The Structure and Function of Immunoglobulins in Man
The cells of the blood, and their supporting fluid are among the most extensively studied biological systems. It is with the fluid portion of the blood that this article is concerned and with a small group of proteins in particular, the immunoglobulins. These show a peculiar and unique behaviour in the presence of other substances called antigens. This behaviour may take the form of combination forming an insoluble precipitate (precipitin reaction), or rendering it more easily phagocytosed by the microphages or macrophages (opsonisation). Other reactions between antibody globulin and antigen are complement fixation in which the four components of complement take part, immune adherence between antigen and adsorbed antibody, and sensitivity reactions such as passive cutaneous anaphylaxis and the Prausnitz-Kustner reaction. However, the central feature of immune reactions is that antibody by definition can only be identified by its reaction with antigen. Identifiable antibody forms only a small part of the total globulin fraction of serum. The remaining globulin may be physically indistinguishable from antibody, but lacks its demonstrably specific activity; this has resulted in the term “Immunoglobulin” being substituted for “antibody” in this article whenever this sense is intended. The greatest barrier to the understanding of the nature of immunoglobulins is the classification used to describe them.
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