68 INTRODUCTION TO IMMUNOCHEMICAL SPECIFICITY 



I shall discuss the nature of the plant agglutinins in Chapter 6. 

 In the meantime may I anticipate by saying that although it is proper 

 to refer to them as agglutinins, as has been done for more than half 

 a century, it would be begging the question to refer to them as anti- 

 bodies. In fact, I do not believe that this is what they are. I have 

 therefore suggested referring to these proteins as lectins, from the 

 Latin legere, t» pick out or choose (Boyd and Shapleigh, 1954a), in 

 order to call attention to their specificity without implying any as- 

 sumptions concerning their origin. I suggested that the term be 

 applied also to those normal antibodies supposedly not the result 

 of antigenic stimulus. But, if Jerne's "natural selection" theory of 

 antibody formation proves to be correct (Chapter 2), it may turn 

 out that the difference between "normal" and "immune" antibodies 

 is not as great as has been thought. In that case the term lectin may 

 come to be restricted to antibody-like plant proteins. In fact, there 

 already seems to be a tendency to use the word in this way. 



No good anti-B lectin is routinely available. Extracts of Sophora 

 japonica agglutinate blood of group B more strongly than that of 

 group A but react too strongly with A to be satisfactory as a labora- 

 tory anti-B reagent (Kriipe, 1953). Euonymus eiiropeiis extracts 

 contain anti-B and anti-H (Schmidt, 1954). Marasmius oreades, 

 which sometimes furnishes a satisfactory, though weak, anti-B, is 

 a small mushroom not commercially available (Elo, Estola, and 

 Malmstrom, 1951). The best anti-B is said to be that from Bandeiraea 

 simpUcijoUa (Makela and Makela, 1956), although the samples of 

 this plant I have tested have been disappointing. 



Because of the absence of an anti-B, lectins are not used routinely 

 in the determination of the ABO blood groups, in spite of the fact 

 that satisfactory anti-A is available from several plants. However, 

 the anti-Ai of Dolichos biflorus and the anti-H of Ulex europeiis 

 make an ideal combination of reagents for the routine determination 

 of the subgroups of A and AB (Boyd and Shapleigh, 1954c), as 

 shown in Table 5-4. Anti-A lectins, especially from lima beans, have 

 had a number of applications in special experiments where a large 

 amount of anti-A agglutinin is needed (At wood and Scheinberg, 

 1958). Testing for H substance in saliva, by inhibition of the anti-H 

 of Ulex (Boyd and Shapleigh, 1954b), has become the preferred 

 method of diagnosing secretors and nonsecretors (Table 5-5). 



