82 INTRODUCTION TO IMMUNOCHEMICAL SPECIFICITY 



simplicifolia became B-specific when tested against cells suspended 

 in 2 per cent glucose. A suitable concentration of galactose makes the 

 anti-(A+B) agglutinin of Calpiirina aurea A-specific (Bird, 1959). 

 Boyd, Everhart, and McMaster (1958) found that some preparations 

 of Baiihinia purpurea were nonspecific (really specific for sugars be- 

 longing to group 2), but could be made N-specific by the addition of 

 D-galactose or other sugars of group 2. Most nonspecific plant ag- 

 glutinins, however, do not develop a new specificity when treated with 

 inhibiting sugars in this way. The three lectins just mentioned would 

 seem to be exceptional in this respect. 



Role of Agglutinins in the Plant 



We do not really know the role in the plant of the proteins which 

 we recognize by their ability to agglutinate certain types of erythro- 

 cytes. In speculating about this role we may follow several lines of 

 thought. 



One possible approach, but in my opinion a naive one, is to as- 

 sume that because the lectins behave like antibodies they are real 

 antibodies. There are several arguments against this assumption : 

 (a) Although the literature on plant immunity is enormous, it has 

 not been demonstrated that plants manufacture antibodies, (b) There 

 is no evidence that the plants have ever been exposed to the blood 

 antigens with which their lectins react. It is extremely unlikely, for 

 example, that Vicia graminea has ever come in contact with the blood 

 group N antigen, (c) Lectins may occur in some varieties of a 

 species and be absent in others. This difference persists even when 

 the varieties are grown in identical environments ; experiments carried 

 out in Puerto Rico have indicated that the difference is hereditary 

 (Schertz, Jurgelsky, and Boyd, 1960). 



Another point of view assumes that the configuration which enables 

 the plant proteins to combine specificially with certain blood group 

 antigens is merely an accidental feature of their structure and that 

 the proteins are present in the seed merely as storage material, or 

 for some similar purpose. 



A third point of view, which I favor, holds that it is no accident 

 that the lectins are adapted to combine specifically with certain car- 

 bohydrates but that their function in the plant is to combine with. 



