440 IMMUNO-CATALYSIS 



in complement-fixation tests for syphilis, was activated by the addition 

 of lecithin and cholesterol. These observations would strongly indicate 

 that lipids exercise strong affinities for specific precipitates and thereby 

 set free "plasma trypsin" by a dissociation reaction : 



Lipid-"trypsin" complex ^ Lipid -j- active "trypsin" 

 (inactive) 



The conception of an analogy between these observations made on 

 humoral systems and the events occurring on intact tissue cells would 

 seem to encounter serious difficulties. Within tissue cells the synthesis 

 of protein catalyzed by a proteinase, perhaps cathepsins, is in a dynamic 

 equilibrium (see p. 52) : Amino acids ^ proteins. The enzyme must 

 therefore be constantly in an active state. To be sure, there might be 

 inhibitors within the cellular environment. Their presence in no way, 

 however, would seem to block the catalytic role of these enzymes in 

 that dynamic state of protein synthesis. Most likely, the synthesis of 

 antibody within the cells is mediated by the same enzymes sup- 

 plemented with antigen. The presence of fixed antibodies in active 

 immunization places, would, therefore, bring them within the im- 

 mediate proximity or in direct contact with proteinases, probably 

 in a complex form. It would seem, therefore, that when a new 

 amount of antigen is reinjected into a passively sensitized or actively 

 immunized animal, causing an anaphylactic shock, a fatal reaction 

 takes place within or on the surface of the cells harboring the factors 

 responsible for a series of events occurring at a speed, in severe cases, 

 reminiscent of an electrical shock. 



The combination of injected antigen with the fixed antibody, 

 forming a complex, could attract and dislodge lipids from the lipo- 

 proteins of the protoplasm and combine with it. Such a course of 

 events can readily cause injury to and disorganization of the cells. 

 As will be discussed below, the mobilization of choline and synthesis 

 of acetylcholine in anaphylaxis may be associated with an effect on the 

 phospholipids of the lecithin type. Cellular metabolism deviating from 

 its normal course can thus cause various other intensified catabolic 

 reactions which have already been considered above. There are 

 numerous observations that in damaged cells proteolysis and gluco- 

 genesis become predominant metabolic reactions. Injured cells would 

 correspond to an in vitro reaction environment where proteinases 



