CHAPTER XVIII 



THE IMMUNOLOGY OF THE PARASITIC PROTOZOA 

 William H. Taliaferro 



The central theme of the science of immunology is the study of the 

 defense meclianisms of the host against the invasion of parasitic or- 

 ganisms or against the introduction of their products or of other in- 

 animate materials. In the present chapter emphasis is placed almost 

 entirely on the defense mechanisms against living parasites. A complete 

 analysis of these mechanisms involves such widely diverse subjects as the 

 origin, nature, and developmental potencies of the cells and tissues of the 

 host, the physiological action and chemical nature of the humoral forces 

 marshaled by the host in defense, the activity of the invading parasite, 

 the chemical nature of the products of the parasite which stimulate the 

 immune processes in the host, and the effects of the various immune proc- 

 esses on the parasite. As protozoan immunity is just one aspect of the 

 general field of immunology, most of the general principles of immunity 

 can be applied directly to the protozoan parasites. Work on protozoan 

 immunity itself, however, has been restricted more or less to the biologi- 

 cal aspects, such as the study of the cellular and the serological mecha- 

 nisms of the host and the effects of resistance on the parasite, with very 

 little emphasis on chemical phases. 



The Physical Bases of Immunity 



Immunity or resistance, in the broad sense, denotes various mecha- 

 nisms of the host which counteract the invasion and the activities of a 

 parasite. It may be manifested as hindrances to the action of invasion, 

 as conditions arising in the body of the host adverse to the parasite, as 

 efforts on the part of the host to make good the deleterious effects of the 

 parasite (as evidenced by the hyperactivity of hematopoietic organs after 

 the destruction of red cells in malaria), or the production of antitoxins 

 in those infections in which toxins are formed. It may be natural (in- 

 nate) or acquired. Natural immunity is generally correlated with non- 



