MESENCHYMAL CELLS 



3 . Eosinophil function 



At this point it seems desirable to return to the question of 

 the significance of the eosinophil cell in immune reactions. 

 Such cells are known to be conspicuous in lesions associated 

 with many types of immunological sensitization especially 

 where antigens derived from helminthic parasites are con- 

 cerned. Speirs (1958) has described systematic studies of 

 the eosinophil content of the peritoneal fluid in mice sub- 

 jected to various types of antigenic stimuli. He found a clear 

 correlation between the number of eosinophils present and 

 the extent of antibody production. The curves given in his 

 paper suggest strongly that the numbers of eosinophils in 

 peritoneal fluid move in parallel with the numbers of anti- 

 body-producing plasma cells in the body. The most striking 

 rise in eosinophils is seen when a secondary antigenic stimulus 

 is given as an intraperitoneal injection of an antigen pre- 

 viously experienced by the mouse. 



Although in most immune responses eosinophils are in 

 a rather small minority, the regularity of their appearance 

 and rise must mean that they are influenced specifically and 

 presumably have some significant role in immunity. Their 

 immediate function is unknown, but if it is established that 

 they respond specifically to a secondary antigenic stimulus it 

 is very difficult to exclude them from membership of the 

 specifically modified clones with which we are concerned. 

 Although some reservations may be necessary — for example, 

 the possibility that the stimulus to the outpouring of eosino- 

 phils is the liberation, from reactive lymphoid cells stimulated 

 by antigen, of some non-specific pharmacologically active 

 substance — Speirs' findings seem to fit better with the as- 

 sumption that the eosinophil and the plasma cell are two 

 specialized products of activated cells which have lodged in 

 appropriate physiological niches. 



Speirs (1958) has suggested that the eosinophil may have 

 a central role in antibody production by constructing tem- 



117 



