Close topographical relationship in alpha foetoprotein (AFP) between a lens culinaris binding glycan and the epitope recognized by AFP-reactive monoclonal antibody, 18H4

Abstract

Summary Monoclonal antibodies 18H4 and 19F12 against alpha-foetoprotein (AFP) were examined by enzyme immunoassay for binding to two forms of AFP that were separated on the basis of the reactivity with lentil lectin (LCA). LCA-binding and LCA non-binding AFP, coated on a solid phase, reacted with 18H4 but reactivity with the LCA-binding species was inhibited by 60% following pretreatment of the AFP with LCA. The lectin was a very poor inhibitor of binding of 18H4 to the AFP which did not interact with LCA. In an alternative binding assay, a polyclonal anti-AFP coated solid phase was reacted with P-galactosidase-labelled 18H4. Pre-treatment with LCA of the LCA-reactive AFP gave 56% inhibition of binding of conjugated 18H4 while little inhibition was achieved with the LCA-nonreactive AFP component. These findings show that the epitope recognised by 18H4 is distinct from the glycan sequence that is reactive with LCA. However, the LCA-binding oligosaccharides occur in close proximity to the 18H4 epitope in the native AFP.

A Lectin-Based Monoclonal Enzyme Immunoassay to Distinguish Fucosylated and Non-Fucosylated α-Fetoprotein Molecular Variants

“…However, such inhibition was not observed when the solid phase was coated with the non-fucosylated AFP. 13 In similar experiments with another reference monoclonal antibody, LCA exhibited little inhibition of the binding of the antibody to the solid phase coated with the fucosylated AFP.…”

“…However, the methods using crossed In our previous study, we selected a monoclonal antibody 18H4 which might be suitable for such a clinical purpose. 13 The binding of 18H4 to the solid phase coated with fucosylated AFP was inhibited by pretreating the solid phase with LCA. However, such inhibition was not observed when the solid phase was coated with the non-fucosylated AFP.…”

“…Purified AFP molecular variants were distinguishable in this monoclonal EIA system in the presence of LCA. 13 The inhibition of the binding of l8H4 to fucosylated AFP can be reasonably explained by assuming that this monoclonal antibody recognizes an epitope of AFP which is closely located to the attachment site of a carbohydrate chain. Treatment with LCA of the fucosylated AFP would result in the binding of this lectin to its fucosylated sugar chain, and prevent 18H4 from binding to the AFP-molecular species by steric hindrance.…”

“…13 The present study describes a clinical application of the simpler method to distinguish fucosylated from non-fucosylated AFP.…”

Alterations of glycan branching and differential expression of sialic acid on alpha fetoprotein among hepatitis patients

“…More sensitive methods of distinguishing AFP between HCC and chronic liver disease have been established by using antibody affinity blotting for the detection of AFP bands separated by LCA affinity electrophoresis [31,32]. Using this method, LCA reactive AFP is a good marker for the differential diagnosis of HCC in the case of chronic liver disease [33][34][35][36][37][38][39]. In addition, it represents a good marker for the early diagnosis of HCC [30].…”