MECHANISM OF ANTIBODY FORMATION 101 



According to the first process, only species specifically related strains 

 of cells cross-fertilize to produce a new strain. No case is known which 

 shows genetic cross-linkings between cells not related species specifi- 

 cally. It would therefore seem improbable that thousands of proteins 

 and thousands of artificial antigens species specifically foreign to the 

 host undergoing immunization are capable of genetically cross-linking 

 with the genes of the host to bring about a building-up process in the 

 antibody producing cells as implied by the theory of Burnet, et al. 



If the life-long immunity to measles and yellow fever viruses persists 

 long after these agents are eliminated (assuming that this is an 

 absolutely proven experimental fact), one may, perhaps, indulge in 

 speculating that these viruses function as "quasi-genetic factors" re- 

 lated species specifically to the globulin synthesizing cells of the host 

 by being derived from them so as to offer a support for the implica- 

 tions of Burnet's theory. However, there are as yet no traces of experi- 

 mental data that smallpox, measles and yellow fever viruses bear 

 species specific relationship to the host cells involved in antibody 

 globulin synthesis. On the other hand, the generally supported idea 

 emphasizes the fact that the observed life-long immunity to these 

 viruses may be due to their multiplication in the host as variants 

 deprived of their properties to cause observable pathological symptoms, 

 as for example, the cow-pox virus, probably arising as a mutation of 

 human smallpox, modified rabies virus produced by brain-to-brain 

 passage in rabbits, and yellow fever virus strain 17D which was evolved 

 by hundreds of passages in tissue culture in media containing em- 

 bryonic tissue from which neural tissue had been removed. The result- 

 ing virus has lost its neurotropic character and has been widely used 

 for human immunization (Theiler and Smith, 1936). 



Reference can be made also to six mutant strains of tobacco mosaic 

 virus each producing characteristic leaf symptoms, and possessing 

 different serological properties and amino acid composition (Knight, 

 Stanley, 1941; Ross, 1941, 1942). These facts would fall in line with 

 our theory of Immuno-catalysis that viruses, like other antigens, 

 function as catalysts in producing specific antibodies. In this role, they 

 do not produce a permanent genetic change in the globulin synthe- 

 sizing cellular enzyme system, but direct certain steps in globulin 

 synthesis to yield antibody globulin. This directive influence continues 

 to function so long as antigen persists (Libby, 1947) as a component 



