2 INTRODUCTION TO IMMUNOCHEMICAL SPECIFICITY 



There is abundant evidence that antibodies play an important role 

 in an individual's resistance to many diseases. For example, the 

 transfer of antibody-containing blood from a convalescent patient to 

 a susceptible person will often make the recipient temporarily im- 

 mune to the disease from which the donor has just recovered (pas- 

 sive immunization). Transfer of antibody from an artificially im- 

 munized animal may be similarly efifective. A decisive change in the 

 sick patient's condition for the better ("crisis") many times coin- 

 cides with the appearance of specific antibodies in the blood. The 

 blood level of specific antibodies is often a fairly reliable index of 

 the degree of a person's immunity. 



It is a characteristic feature of antibodies that they react with the 

 antigen which caused their production ; in fact, new proteins appear- 

 ing in the circulation which do not react in a detectable way with 

 the antigen responsible for their production in general are not called 

 antibodies. In a few instances antibodies have been observed which 

 reacted wath an antigen different from the one which caused them to 

 be produced and did not react visibly with their own antigen (Hooker 

 and Boyd, 1933; Glutton, Harington, and Yuill, 1938), but these are 

 exceptions. 



The reaction of antibodies with their antigen can have one or more 

 of a number of effects : (a) Antibodies to toxins may neutralize the 

 toxity of the antigen, and antibodies to viruses may neutralize the 

 infectivity of the antigen, (b) Antibodies to soluble proteins and 

 other soluble antigens may precipitate their antigen (Fig. 1-1). (c) 

 Antibodies to microorganisms and foreign erythrocytes may cause 

 the antigenic cells to stick together (agglutinate) (Fig. 1-2). (d) 

 Antibodies to erythrocytes and certain microorganisms may cause 

 the antigenic cells to disintegrate. This phenomenon is called lysis, 

 and for its production the cooperation of certain normal components 

 of plasma, collectively called complement, is required, (e) Anti- 

 bodies to certain microorganisms, aided by complement, may cause 

 the death of the antigenic cells (bactericidal effect), (f) Antibody 

 to certain microorganisms causes the capsules of the microorganisms 

 to swell visibly. This phenomenon is generally referred to by its Ger- 

 man name Quellung. (g) Gombination of antibody with micro- 

 organisms and other foreign cells generally makes the invaders more 

 attractive to the leukocytes of the patient's circulation and thus pro- 



