Griffonia lectin has moderate to mild reactivity with both A and B antigen, but more importantly, reacts with Lewis B antigen (a rare occurence). As I've mentioned, Lewis typing can be a 'quick and dirty' way to determine secretor status. Basically, we all start off making Lewis A (unless you are one of the .5% of the world that makes no Lewis antigen, a topic for another post) but secretors convert all their Lewis A antigen into Lewis B, so Non-secretors are Lewis A+ Lewis B- and secretors are Lewis A- Lewis B+.
This Griffonia is more of a problem in Type A and B Secretors, than in A or B Non-secretors.
Why is this important?
Most of the newer type tryptophane supplements ('5HT') are derived from Griffonia.
J Mol Biol 1993 Apr 5;230(3):950-65
Structures of the lectin IV of Griffonia simplicifolia and its complex with the Lewis b human blood group determinant at 2.0 A resolution.
Delbaere LT, Vandonselaar M, Prasad L, Quail JW, Wilson KS, Dauter Z