Which one of the following hypotheses may be sufficient to explain non precipitation in antigen-antibody system?: (A) The antigen has a multivalent determinant, (B) The antigen has a single, non-repeated determinant, (C) The antibody has been cleaved to divalent Fab' ligands, (D) The antibody has been cleaved to divalent Fab'2 ligands
Answer is C. Neither monovalent antigen nor monovalent antibody (Fab:) can form a precipitin lattice. An antigen molecule containing closely repeating antigen determinants (e.g., a polysaccharide or a multi chained polymeric protein), can bind antibody to two determinants on a single particle; this "monogamous bivalency" inhibits precipitation. Fab2 divalent antibodies can precipitate antigens, though they lack Fc portions.