Alexin

ALEXIN (from Greek alexo- I protect), a name given by Buchner to protective substances whose presence, according to his theory, determines the bactericidal properties of sera. Metchnikoff refuted this theory; it turned out that alexin does not play a protective role. However, when Bordet clarified the enormous role of the substance described by Buchner in immune reactions, the name A. was retained for this substance, which was later changed by the German school to 'complement.' Bordet showed that in the phenomena of lysis occurring in immune reactions, two substances participate: one - present in all fresh normal sera, non-specific and easily destroyed by heating - alexin, and another - appearing as a result of immunization, significantly more stable - substance sensibilisatrice. According to Bordet's view, A. is adsorbed by antigen sensitized by substance sensibilisatrice; according to Ehrlich, alexin (called by him 'complement') chemically combines with substance sensibilisatrice (amboceptor), which in turn combines with antigen. At present, it has been definitely established that A. combines in immune reactions according to an adsorption curve, which contradicts Ehrlich's views. Metchnikoff proposed to call substance sensibilisatrice and A. fixator and cytozyme, in order not to predetermine by name the nature of their combination with antigen. These names, however, did not take root in the literature. The doctrine of the multiplicity of A. (Ehrlich), according to which each animal species has many different A. adapted to various amboceptors, as well as the doctrine of macro- and microcytozymes (Metchnikoff) are now defended by no one, and most stand on the point of view of the unitary concept (Buchner, Bordde), recognizing the existence of only one alexin acting in all reactions. The main characteristic of alexin is its lability: heating for half an hour to 56°, standing at room temperature, shaking, addition of acids and alkalis, ultraviolet rays, rays of the visible spectrum, various products formed in large quantities in pathological conditions of the body - lactic acid, acetone, etc. - all this easily destroys A. With such lability of alexin function, the difficulty of methods for its preservation is clear. The most satisfactory methods in this respect should be considered the addition to A. of table salt (Friedberger), sodium acetate (Rhami) and boric acid (Ginzburg). Ferrata, Brand and others showed that the alexin function of serum is connected both with its globulins and with its albumins. The albumin part causes hemolysis of sensitized antigen only after it has been acted upon by the globulin part, therefore the globulin part is called the intermediate (Mittelstück), and the albumin part - the terminal (Endstück). A. is adsorbed, besides the system: antigen+antibody, also by all sorts of colloidal solutions. This adsorption apparently proceeds in the same way as the adsorption of A. in immune reactions. Many opinions have been expressed regarding the nature of A. Some considered it an enzyme, others pointed to the analogy of the action of lecithin and complement in experiments with cobra lecithin. According to Liebermann and Noguchi, A. is a protein-soap compound, according to Landsteiner - a lipoprotein. But most authors who have recently studied the nature of alexin come to the conclusion that alexin is not any labile chemical substance, and that the alexin function of serum is an expression of its special colloidal state (Hecht, Klopstock, Barykin, Zilber). This view follows from a series of experiments in which it was shown that any change in the colloidal state of serum is accompanied by its inactivation, and in a number of cases, when the serum returns to its previous state, its alexin function also returns. Such are the experiments with careful heating of serum, with increasing and decreasing the concentration of salts in it, with drying, shaking, etc. In these experiments, A. behaves like a typical hydrophilic colloid, which can be brought to aggregation by a whole series of conditions, but which can more or less regenerate its state if the aggregation process does not go too far. One can compare the alexin function of serum to the ability of colloidal platinum to decompose hydrogen peroxide. A change in the state of colloidal platinum clearly affects this ability; returning to the original colloidal state restores this property to it. A clear expression of the aggregation of colloidal particles occurring during inactivation of A. is the decrease in surface tension of serum, which inevitably accompanies any inactivation, regardless of the causes that caused it. The phase of serum with which the alexin function is connected is more coarsely dispersed than the phase with which antibodies are connected. This is evident both from experiments with filtration (Trouin) of the corresponding mixtures, and from experiments with diffusion of these mixtures (Kabelik): alexin passed everywhere later than antibodies or was completely delayed (filtration). These facts also explain the complex structure of the phase with which the alexin function is connected (Mittelstück and Endstück). In the adsorption of A., one of the phases of serum is actually adsorbed, due to which the colloidal state of the system is disrupted and its alexin function disappears. Based on these facts and concepts, A. can be defined as a property of serum that determines the peptization of antigens sensitized by corresponding antibodies, functionally connected with its colloidal state and easily disappearing depending on various physical and chemical causes.