Actions and Interactions of Immunoglobulins in Immune Tissue Damage

Abstract

This chapter discusses the actions and interactions of immunoglobulins in immune tissue damage. Immune tissue damage may result either from immunotoxic reactions or from hypersensitivity reactions. In immunotoxic reactions, the antigen inducing the immune reaction belongs to a cell or to a tissue structure (the target), which will undergo the consequences of the reaction. These consequences result from the direct action of the immune agents (cells of free antibodies) specifically binding to the target. Antibody-mediated hypersensitivity reactions may be caused by antibodies secondarily bound to the surface of specialized cells (such as mast cells), giving rise (after having reacted with the corresponding antigen) to anaphylactic manifestations or they may result from the interaction of free-circulating antibodies with the corresponding antigens, giving rise to the various manifestations of immune complex disease. Three considerations bring some degree of complexity to this simple scheme of actions and reactions. First, there are the different biological properties of the various immunoglobulin classes of antibodies. These biological properties are incompletely known. They are exhibited after activation of the antibodies by the antigen or by aggregation. They mainly consist in triggering sequential activations at the level of enzymatic systems or on cell surfaces, resulting in synthesis and release of substances active in inflammation. Second, there are the interactions between immune agents (that is, between sensitized cells and antibodies or between antibodies of different classes). Interactions can operate synergistically or antagonistically following mechanisms to be more precisely defined. Third, there is the degree of target accessibility in vivo to the specific immune agents. A differential accessibility would be of importance because of the different biological properties of the immune agents. This chapter considers these three features in succession as they apply to various types of tissue lesions such as Arthus, autoimmune, allotransplantation, and cellular hypersensitivity.