IMPLICATIONS OF CLONAL SELECTION 



same route. Similarly if histology is any guide, lymphocytes 

 and their products must continually be oozing into the cavity 

 of the appendix and the crypts of the tonsil — presumably 

 for a purpose. 



There are two other situations where plasma cells are 

 reported to be conspicuous. The first is in relation to the 

 mammary gland. Campbell, Porter and Petersen (1950) 

 observed in the bovine udder at the time of calving numerous 

 plasma cells in the interstitial tissue between the lobules of 

 the gland. At this time the colostrum with its high content 

 of antibody is being produced and there is perhaps special 

 likelihood of infection being present in the gland. Some 

 weeks later biopsy of the lactating udder showed no such 

 accumulation. The second is from an observation of Bowden 

 and French that in children dying after influenza the sero- 

 mucous glands of the trachea and bronchi show interstitial 

 accumulations of plasma cells (French, 1958). 



All these findings seem to point in a specific direction. The 

 suggestion that these varied lymphoid accumulations have 

 some sort of protective function has been current for many 

 years but there has never been an adequate immunological 

 background to provide any detail to the contention. 



In terms of the clonal selection theory, any lymphocyte in 

 the submucosal region which is ' tuned ' to react with a deter- 

 minant from an infective agent in the region will tend to 

 be activated and fixed in the tissue. By a natural process of 

 selective proliferation the population of lymphoid cells in the 

 submucosal accumulations will come to carry predominantly 

 reactive sites corresponding to antigenic determinants that 

 have been associated with past micro-organismal invasion 

 of the surface in question, perhaps specially with viral in- 

 fection. If these sources of antibody are continually pro- 

 viding an outflow to moisten the surface, there is available 

 a simple explanation of local immunity to polio and other 

 intestinal viruses. 



The danger of invasion must be common to the whole 



84 



