IMPLICATIONS OF CLONAL SELECTION 



4. Local immunity 



This is a term which has been used in rather indefinite 

 fashion, but for the present purpose it will be applied essen- 

 tially to the only example which has been well studied in 

 recent years — intestinal immunity against polio viruses. The 

 evidence is clear that by immunization with formalin-killed 

 polio vaccine, circulating antibody is induced and effective 

 immunity provided against the paralytic disease. No resis- 

 tance is induced to implantation of homologous virus in the 

 bowel. This so far has been induced only by actual intestinal 

 infection with virulent natural virus or by the administration 

 of attenuated variants. To date there is virtually no factual 

 knowledge of the physiological and serological basis of this 

 local immunity. It appears to be type specific and therefore 

 to be mediated by an immunological mechanism. The only 

 fragment of probably relevant data is that the virus can 

 multiply in the lymphoid tissue of Peyer's patches, but it will 

 be taken as axiomatic that this immunity is mediated by 

 mesenchymal cells and/or the globulins they produce. 



It is characteristic of all mucous surfaces which are in 

 contact with a contaminated or potentially contaminated 

 environment that in the submucosal tissue there are collec- 

 tions of lymphoid and plasma cells ranging from scattered 

 cells to single lymph follicles and larger accumulations such 

 as the Peyer's patches of the small intestine. The final stage 

 is reached in the specialized accumulations of lymphoid 

 tissue, the tonsils and the appendix. In all these situations 

 there is usually clear evidence that lymphocytes or any pro- 

 duct of their functioning can readily pass into the lumen of 

 the viscus or on to the surface exposed to the environment. 

 Over a Peyer's patch, for instance, the intestinal epithelium 

 is heavily infiltrated with lymphocytes, many of which are 

 clearly passing into the intestinal lumen. If antibody is being 

 produced by the plasma cells, which are numerous in the 

 Peyer's patches, it must be leaking into the lumen by the 



83 6-2 



