MODULATION OF THE ANTIGENIC REACTIVITY OF THE CITRUS TRISTEZA VIRUS COAT PROTEIN

Trapping properties of a panel of monoclonal antibodies (Mabs) raised against citrus tristeza virus (CTV) were analyzed in an indirect doubl e-antibody sandwich ELISA (I-DAS-ELISA), These antibodies had been pre viously assigned by serological specificity into five groups (I to V). Mabs from group V, which are directed to conformational epitopes, tra pped significant amounts of virus antigen from CTV-infected plant tiss ue at IgG concentration above 10 ng/ml. Mabs from groups I to IV, whic h are directed to linear, continuous epitopes, performed poorly as coa ting antibodies, even at a 1 mu g/ml concentration of the IgG's, indic ating that the respective linear epitopes were inaccessible. However, when Mabs from groups I to IV were combined with a small amount of Mab s from group V, a substantial increase in trapping of the CTV antigen was recorded, In this 'two antibody-binding assay' previously cryptic, linear epitopes of the CTV CP apparently became accessible to the Mab s from groups I to IV. Modulation of the antigenic reactivity of the C TV CP was also recorded upon binding of the Mabs directed to the confo rmational epitopes in solution. Induced exposure of the linear epitope s of the CTV CP was revealed in 'two antibody-binding assays' with pai rwise combinations of different mouse IL labs and several rabbit and c hicken polyclonal antisera with different serological specificities, i ncluding antisera to bacterially expressed CP fragments, This mixed co ating in I-DAS-ELISA resulted in substantially increased efficiency of the virus antigen trapping by antisera produced against bacterially e xpressed protein fragments and an increased sensitivity of the CTV det ection after optimization of the ratio between conformational and line ar antibodies. (C) 1997 Elsevier Science B.V.