840 IMMUNOLOGY 



cells in local defense. The lymphocytes and the monocytes migrate from 

 the blood vessels, as do the heterophils; but unlike the heterophils they 

 are long-lived, may multiply in the tissues, may develop into macro- 

 phages with phagocytic potencies, and from macrophages may progres- 

 sively develop into fibroblasts with reparative functions. As macro- 

 phages, they, together with the macrophages previously present in the 

 area, actively phagocytose and digest certain invading organisms, remove 

 cellular and other debris, and after the acquisition of immunity probably 

 elaborate antibodies which aid in phagocytosis. When large bodies are 

 present, the macrophages may fuse to form foreign body giant cells; 

 when microorganisms are indigestible, they may form giant cells around 

 them, such as the epithelioid cells of the tubercle; or, when large areas 

 are necrotic, they may surround the area, become transformed into fibro- 

 blasts, and effectively wall it off. The fibroblasts, both those of the local 

 area and those arising from macrophages, react slowly and probably 

 play an active part only in the later stages of local inflammation during 

 regenerative and reparative processes, the formation of scar tissue, and 

 the walling off of foreign bodies. 



Several other cells may come into play, generally during late stages 

 in the defense reaction. Of these, the eosinophils seem to play a part in 

 the detoxification of foreign proteins and their disintegration products 

 and are particularly prominent after the body has become sensitized to 

 the proteins. Like the heterophils, they do not multiply and cannot de- 

 velop into other cells of the area. Some investigators believe that the 

 plasma cells are also associated with the detoxification of foreign ma- 

 terials. They are not phagocytic, do not seem to have any developmental 

 potencies, and proliferate rarely, if at all. The exact function of the 

 basophils is unknown. 



Ordinarily, when the stimulant is distributed over a large part of the 

 body, the reaction is designated as a general defense reaction, in contra- 

 distinction to the local defense reaction just described, but as a matter 

 of fact such distribution usually signifies that the stimulant is in the 

 blood stream and is combated by macrophages of organs most closely 

 associated with the blood, such as the spleen, liver, and bone marrow. 

 In some cases, as in malaria, these general reactions can actually be con- 

 sidered local ones in strategically placed organs (see W. H. Taliaferro, 



