OPSONINS AND BACTERIOTROPINS 235 



Opsonins and Bacteriotropins. 



Wright and Douglas (1903, 1904) named and described the opsonins — thermo- 

 labile, relatively non-specific substances, occurring in normal serum, acting on a 

 variety of bacteria and rendering them liable to phagocytosis by leucocytes. 

 Neufeld and Rimpau (1904, 1905) named and described the bacteriotropins — thermo- 

 stable antibodies occurring in the serum of immunized animals, acting specifically 

 on the bacteria against which the animals had been immunized, and rendering them 

 liable to phagocytosis. 



The mode of action of the bacteriotropins is clearly analogous to that of the 

 precipitins, agglutinins and lysins. Like these antibodies they are relatively 

 thermostable. Like them they unite specifically with an antigen carried by the 

 bacterial cell. We can safely assume that the anchoring of the antibody globulin 

 to the antigen alters the condition at the cell surface in such a way as to make it 

 easier for the leucocytes to engulf the bacteria, just as it makes the bacteria salt- 

 sensitive, and, in certain cases, renders the cell membrane more permeable. It 

 would appear that one important factor is a lowering of the negative charge, and 

 hence of the difference in electrical potential between the bacteria and the surround- 

 ing fluid. 



Falk and Matsuda (1926) found that alterations in the charge carried by pneumococci 

 induced by the addition of lanthanum nitrate or sodium oleate had a striking effect on 

 the phagocytosis of these organisms, and Broom and Brown ( 1930) were able to decrease 

 the phagocytosis of staphylococci, previously sensitized with serum, by preventing the 

 usual reduction in surface charge by the addition of potassium ferrocyanide. Mudd and 

 others (1929) studied the changes induced by specific antisera in four strains of acid-fast 

 bacilli. They found that sensitization (a) increased the cohesiveness of the bacilli ; (b) 

 decreased the electric charge, as evidenced by a decrease in velocity of cataphoresis ; 

 (c) decreased the " wettability " of the bacilli by oU, as evidenced by their distribution at an 

 interface between tricaprin and normal saHne, and {d) increased their susceptibility to 

 phagocytosis. 



Bacteria may be opsonized by non-specific substances, tanning agents like gallotannic 

 acid (Reiner and Fischer 1929, Reiner and Kopp 1929), tannic acid (Freud 1929) and 

 alum, chrome and ferric salts (Neufeld and Etinger-Tulcyznska 1929). Gordon and 

 Thompson (1936) and Gordon and Atkin (1938) made a systematic study of the artificial 

 opsonization of Salm. typhi and Staph, aureus. Metallic tanning agents appeared to 

 act by combination witli carboxyl groups, the vegetable tannins with the basic groups 

 of the bacterial proteins. The two organisms differed in their susceptibihty to certain 

 agents ; StajJi. aureus, perhaps by virtue of having on its surface more acidic groups 

 than Salm. tyj)hi, was more susceptiljle to protamine, a highly basic protein. These 

 authors noted that while potassium oxalate and distilled water reversed opsonization, 

 opsonization by specific serum was more difficult to reverse. 



There remains the problem of the relation of the normal opsonins of Wright 

 and Douglas to the bacteriotropins of Neufeld and Eimpau. In their thermolability 

 the opsonins resemble complement ; and their identity with this serum constituent 

 seemed at first to be rendered probable by the observation of Muir and Martin 

 (1906a) that such complexes as red cells and haemolysin, a protein antigen and its 

 corresponding antibody, or bacteria and a specific antibacterial serum, all removed 

 the opsonin from a normal serum, at the same time as they removed the com- 

 plement. The observation of Neufeld and Hune (1907), that absorbing a normal 

 serum with yeast had a similar double effect, seemed to point in the same direction. 

 But there were difficulties in this simple conception. The normal serum opsonins 



