CHAPTER LXVII 

 LOCAL AND TISSUE IMMUNITY^ 



FREDERICK P. GAY 



Columbia University 



GENERAL CONSIDERATIONS 



Anyone who has carefully followed the evolution of the science of immunology 

 'nust feel certain that in many of the protective processes there is concerned some 

 third, and as yet not clearly understood, factor in addition to the mobile polymorpho- 

 nuclear phagocytes of the bloodstream and the antibodies. 



Natural or "innate" immunity, which sufi&ces to protect normal animals against 

 slight or moderately virulent infectious agents, may in general be ascribed to the 

 activity of the polymorphonuclear leukocytes of the circulating blood. Acquired im- 

 munity, whether expressed actively in a recovered or actively immunized animal, or 

 passively through transfer of the serum of hyperimmunized animals, involves certain 

 new and enhanced physiological activities. These activities are expressed in the re- 

 action products of serum usually designated as ''antibodies." These antagonistic 

 substances are characterized by their ability to unite in a specific manner \vith the 

 antigenic substance that has given rise to them. In the case of the antitoxins, this 

 union is followed by a direct neutralization, although usually not by the destruction, 

 of the corresponding toxin. The other antibodies, whether they be regarded as a unit 

 or as multiple, unite with the corresponding antigen, characteristically a bacterium, 

 although they do not in themselves destroy it. Such a "sensitized" antigen is however 

 remarkably susceptible to the ferment-like action of the alexin or complement which is 

 a normal constituent of plasma and serum. And, what perhaps is equally important, a 

 sensitized (tropinized or opsinized) bacterium is rendered readily phagocytable by 

 normal leukocytes, which alone may be ineffective against this particular microbe. 



But all these facts, important as they are, do not suffice to explain the numerous 

 phenomena of immunity. They are in particular inadequate in explaining some of the 

 most pronounced instances of acquired immunity. Smallpox immunity and the im- 

 munity which follows recovery from typhoid fever, for example, are not to be ac- 

 counted for either by the activity of the polymorphonuclear leukocytes or yet by the 

 action of antibodies. In spite of the importance of antibodies as indicative of a pro- 

 tective reaction, a very marked immunity may exist without their presence; and their 

 presence alone does not insure protection. 



It is evident, therefore, that by a process of exclusion, we are forced to consider 

 the more or less fLxed tissues of the body to find an explanation for certain phases of 

 immunity. 



I The reader is referred to previous reviews by the author which discuss in fuller detail the 

 historical development and earlier conceptions in this subject: (i) /. Immunol., 8, i. 1923; (2) 

 Physiol. Rev., 4, 191-214. 1924; (3) Arch. Path. &' Lab. Med., i, 590-604. 1926. 



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