CHAPTER LXVI 

 PHAGOCYTES AND PHAGOCYTOSIS IN IMMUNITY 



W. B. WHERRY 



University of Cincinnati 



The story of the ardent contest between the champions of the humoral theory of 

 immunity and those who maintained that certain body cells played an equally impor- 

 tant role has been told by Metchnikoff.^ 



Briefly, there was established the fact that when foreign bodies of a varied nature, 

 including parasitic micro-organisms, gain entrance to the tissues of the metazoa they 

 are invested by certain cells derived from the fixed tissues or from the circulating 

 blood. In the case of invasion by parasites, when ingestion (phagocytosis) was fol- 

 lowed by digestion the host recovered, otherwise it succumbed. Metchnikoff demon- 

 strated that the digestive process within the phagocytes was quite analogous to that 

 which goes on within many protozoa. He distinguished between motile phagocytes, 

 derived from the blood, and fixed phagocytes — certain connective tissue cells, en- 

 dothelial cells, splenic pulp cells, and phagocytic cells found in the lymph nodes and 

 in the neuroglia. The polymorphonuclear cells of the blood he termed "microphages" 

 and their proteolytic ferment "microcytase." All the other phagocytes were classed 

 as "macrophages" and their digestive ferment "macrocytase." 



He clearly recognized the fact that when a host was invaded by certain parasites 

 and responded by exhibiting an "acute inflammation" the microphages were most often 

 concerned in the defense, and that the macrophages only appeared later to clear up 

 the debris and so aid in the process of repair. Where, however, the reaction was of 

 such a nature as to produce "chronic inflammation," the macrophages played a dom- 

 inant role. 



Many investigators questioned the ability of the phagocytes to kill the parasites. 

 Some maintained that the parasites were killed first by normal or acquired bacteri- 

 cidal substances present in blood serum and then ingested and removed as so much 

 foreign debris. Metchnikoff was forced to admit the influence of some factors present 

 in blood serum or plasma and termed the substances "stimulins" because he believed 

 they stimulated the leuckocytes directly. 



The more important steps in the growth of our knowledge may be summarized as 

 follows: Denys and Le Clef^ noted that the recovery of immunized rabbits from 

 streptococcus infection was apparently due to phagocytes and believed that ingestion 

 was made possible by the antitoxic action of immune substances. Mennes' and many 

 others noted that phagocytosis only occurred to a considerable degree in the pres- 

 ence of immune serum. 



'Metchnikoff, Elie: L'lm in unite dans les maladies infcctieuses. Paris, igoi. English trans. 

 Cambridge University Press, 1907. 



^ Denys, J., and Le Clef, J.: Cellule (Lierre and Louvain), 11, 175. 1S95-96. 

 3 Mennes, Fr. : Zlschr.f. Hyg. u. Injektionskrankh., 25, 413. 1897. 



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