Pharmacological aspects of immune reactions

"Immunopharmacology" evolved as a field of research in its own right when it was appreciated that pharmacological methods can contribute to the understanding of immune mechanisms on the one hand or can be used to influence or even control immune reactions at all stages and levels. The best studied subjects of immunopharmacology are release and effects of the chemical mediator substances which are responsible for the reactions of effector cells thus causing the clinical symptoms in allergic or inflammatory diseases. In the type I allergic (anaphylactic) reactions the primary target cells are tissue mast cells or basophil granulocytes which discharge their granular contents upon interaction of immunoglobulin E fixed to their surface with the specific antigen or--in the anaphylactoid reaction--upon stimulation with an appropriate chemical substance (so-called histamine-liberator). In both cases the stimulus leads to an influx or intracellular shift from one compartment to another of calcium ions, which in turn trigger membrane fusion and degranulation. This process can vary from a physiological secretion (in the case of IgE-antigen-interaction) to a pathological cytolysis (in the case of high concentrations of activated complement components or other chemical histamine releasers). As long as it is secretory it is subject to vegetative and hormonal modulation and regulation, mainly by catecholamines and other substances which increase cellular cAMP levels or inhibit calcium fluxes. Although cholinergic stimuli under certain circumstances induce mast cell degranulation and histamine release no definite role has yet been established for cholinergic mechanisms in type I allergies. Type II (Cytotoxic) and type III (immune complex mediated) allergies share the complement requirement. As far as mast cells and basophils are involved in such reactions their sensitivity towards pharmacological modulators is comparable to reactions induced by chemical histamine releasers. Otherwise these types of allergic reactions are dominated by phenomena of general inflammation. In those mainly cytotoxic effects of lipases and hydrolases are involved. cAMP active agents have, therefore, only limited modulating effects and steroid hormones are more effective in inhibiting the acute lesions in type II and III allergies. Only during the last decade the involvement of chemical mediators in type IV (cellular immunity) allergic reactions has been appreciated. 26 different factors called lymphokines have been discovered and classified as mediators of cellular immune reactions. However, rather little is yet known about their chemical nature and about the influence of drugs on their production or action.