IMMUNOLOGY 837 



of macrophages associated with immunity, i.e., "hyperplasia of the 

 reticulo-endothehal system," is due to the prohferation of macrophages 

 or cells of the reticulo-endothelial system. This is an admitted source, 

 but detailed studies of a wide variety indicate that most of the new 

 macrophages arise from lymphocytes, with or without the intervention 

 of a monocyte stage (see PI. 4). In order to include both macrophages 

 and all of their precursors under one term, which would indicate the 

 cytogenesis of macrophages from agranulocytes (lymphocytes and 

 monocytes) as well as from reticulo-endothelial cells, W. H. Taliaferro 

 and Mulligan (1937) proposed the term, lymphoid-macrophage system. 

 This term includes the mononuclear exudate cells, or Maximow's poly- 

 blasts, which form the cellular exudate in inflammation. 



ANTIBODIES AND ANTIGENS INVOLVED IN IMMUNITY 



Infective organisms, derivatives of them, or other foreign, colloidal, 

 protein materials can generally act as antigens. When an antigen is intro- 

 duced parenterally into an animal, it calls forth a substance in the blood 

 of the animal, known as an antibody, which will react with the antigen 

 specifically in vivo and generally iti vitro and is passively transferable. 

 Such an antibody is often termed an immune antibody, to differentiate it 

 from natural antibodies, which sometimes exist in blood without im- 

 munization. Serum from the blood of an animal containing an antibody 

 is known as antiserum. Some antibodies or antiserums, in addition to 

 reacting with their specific complete antigens, may also react with iso- 

 lated carbohydrate or lipoid parts of the antigen iti vitro. These sub- 

 stances have been differentiated from true antigens by the terms haptenes 

 or partial antigens, since they generally do not stimulate the production 

 of antibodies in vivo. Both complete antigens and haptenes have been 

 isolated in high states of purity. Antibodies result from antigenic stimu- 

 lation and are metabolic products of cells. Thus the amount of circulat- 

 ing antibody is often decreased by removing the spleen, which is rich 

 in cells of the lymphoid-macrophage system, or by filling the macro- 

 phages along the blood stream with colloidal or particulate matter. 

 Furthermore, antibodies undoubtedly represent definite substances which 

 are closely associated with the globulin fraction of the serum. It is, how- 

 ever, impossible to say at present whether they are actually globulins 

 and, if they are globulins, whether they are new globulins or the regular 



