OPSOMNki 207 



increased in pregnancy,^"*^ and hence the reaction with placenta is more 

 marked tlian witli the serum of non-jiregnant individuals. But simply 

 sliaking nornud serum with kaolin or other foreign substances may 

 cause it to give strong reactions with placenta antigen (AVallis) . 



OPSONINS 40 



The correlation of phagocytic and serum immunitj' was accom- 

 plished when A. E. AV right showed that, before any considerable 

 phagoej'tosis of bacteria can take place, the bacteria must first be 

 acted upon by serum, which in some way prepares them to be in- 

 gested by the leucocytes. The hypothetical substances accomplish- 

 ing this sensitization of the bacteria were called opsonins by Wright, 

 and the}' exist to a certain extent in normal serum, being increased 

 by immunization. Not only bacteria, but cellular elements in general, 

 including especially red corpuscles, and even unorganized particles 

 (such as melanin),*^ are sensitized for phagocytosis by opsonins. 

 Probably phagocytosis by endothelial *- and other cells also requires 

 sensitization of the bacteria by opsonins. Although there have been 

 many expressions of the opinion that the opsonins are not distinct 

 antibodies, but are identical with agglutinins, bacteriolytic ambo- 

 ceptors, or other antibodies, there is much evidence to the contrary.*^ 

 There are two opsonizing elements in serum, one thermostable and one 

 thermolabile, it being the former which is increased during immuniza- 

 tion ; the thermostable element unites firmly with the object whieli is 

 to be opsonized, while the thermolabile element seems to remain free 

 in the fluid (Hektoen)." 



It would seem that opsonization and phagocytosis constitute but one 

 of a series of similar processes by which foreign proteins are removed 

 from the blood and tissues; i. e., by lysis by extracellular enzymes 

 when this is possible, as it is vsdth simple protein aggregates (albu- 

 minolysis) and with some of the more labile cells (hemolysis, bacterio- 

 lysis) ; but in the case of more resistant structures, notable Gram- 

 positive cocci and acid-fast bacilli, extracellular lysis being unsuc- 

 cessful, these protein structures are taken within the cells where a 



30g See Sloan, Amer. Jour. Physiol.. 1915 (39), 9. 



40 Bibliography given bv Xeufeld, Kolle and \Yassermann's Handbuch, 191.3 (2), 

 440. 



41 Shattock and Dudgeon. Proc. Eoyal Soo. (B), 1908 (SO). 165. 



42 Briscoe, Jour. Path, and Bact., 1907 (12), 66. See also ]\Ian\varing and Coe, 

 who found that the Kupffer cells can take up onlv opsonized pneuinococci (Proc. 

 Soc. Exp. Biol., 1916 (13), 171). 



43 See Hektoen. .Jour. Tnfec. Dis., 1909 (6). 7S: 1913 (12), 1. 

 44Sawtchenko (Arch. Sci. Biol., 1910 (15), 145: 1911 (16), 161) holds that 



there are two steps in phagocytosis: (1) Fixation of the bacteria to the leuco- 

 cyte because of modification of surface tension by the fixative substance (opsonin 

 or aniboceptor-coniplement complex); (2) Ameboid motion of the phagocyte; 

 an entirely independent phenomenon. Neither phase of phagocytosis can occur 

 in the absence of electrolvtes. 



