250 THE ANTIOEN-ANTIBODT REACTIONS 



and Boyd (194:1a) suggest that they may be due to {a) the formation of antibodies 

 to minor antigenic determinants, (6) the increase in the number of reactive groupings 

 on the antibody, or (c) the wider affinity of the combining groups, due to the forma- 

 tion of a larger and more complex reactive patch on the antibody surface. The 

 broadening may be accompanied by a change in the nature of the globulins. Kaffel, 

 Pait and Terry (1940) found the earlier, less avid antibody to be associated with 

 the water-insoluble globulins, the later, avid antibody with water-soluble globulins. 

 The evidence of heterogeneity found among fractions of antiserum, made by pre- 

 cipitation with salts is less convincing, because it is difficult to exclude artefacts, 

 but the differences, noted above, in reactivity displayed by electrophoretic fractions 

 of antisera cannot be lightly dismissed. 



Goodner and Horsfall (1937) obtained other evidence of heterogeneity, in antipneumo- 

 coccal sera. In several rabbit antisera, the ratio of precipitin content to protective power 

 was constant, but in horse antisera it was inconstant. Moreover, in individual sera of 

 both species the protective power of antibody left after some of it had been precipitated 

 by antigen varied with the amount of antigen added, though the variation was much 

 greater in the horse. When horse antiserum was fractionated, the pseudoglobuhn was 

 found to contain antibody with a protective power only one-seventh that in the euglobuhn 

 fraction, though the pseudoglobuhn antibody was far more reactive as precipitin. In 

 an electrophoretic fractionation of dijjhtheria antitoxin, the antibody }' component com- 

 bined with twice as much nitrogen per flocculating unit as that from the (i component. 

 Goodner, Horsfall and Bauer (1938) also demonstrated heterogeneity in the size of anti- 

 body particles in both rabbit and horse antisera. For example, in horse antisera very 

 large particles, corresponding to a pore size of 175 m/j, in a collodion membrane filter, were 

 found in concentrated serum, and of 83 7n/n in native serum. Dilution in saline reduced 

 the particle size in both types of serum. 



The antibodies formed in response to the injection of what is apparently a single 

 antigen may also display varying kinds of serological specificity. Thus, Landsteiner and 

 van der Scheer (1939), working with proteins modified by coupling to pentapeptides 

 (made up of various combinations of glycine and leucine), showed that aU the antibodies 

 produced in response to any one pejDtide-protein were absorbed by the same peptide 

 coupled to an antigenicaUy unrelated vehicle, namely erythrocyte stromata. Neverthe- 

 less, varying amounts of the total antibody could be removed from the sera prepared 

 against one peptide, by absorption with stromata to which one of the other peptides 

 had been coupled. Absorption occurred even when the absorbing peptide could not 

 conceivably have been a breakdown product of the antibody-producing peptide. 



It is clear that in horse sera, at any rate, apparently monospecific antibodies 

 display heterogeneity both with regard to their reactivity as antibodies, and to 

 their other physicochemical properties. Monospecific rabbit antibodies appear to 

 be less heterogeneous, at least functionally. Indeed, the degree of homogeneity 

 may be surprisingly high. Thus, Hershey, Kalmanson and Bronfenbrenner (1943) 

 record an analysis of a number of rabbit anti-phage sera, with a 25-fold range 

 of combining power, in which there was full correlation between three varying 

 qualities, specific rate of phage neutralization, neutralizing capacity, and precipi- 

 tating capacity ; and no tests revealed any heterogeneity of antibody in any 

 one serum. 



The Valency of Antibody. 



It is obvious that the conception of monospecific antibody molecules of different 

 valencies will help to explain some of the observed heterogeneity of antibody in 

 the natural state. As we have seen, the assumption of multivalent antibody is 



