Monoclonal antibodies to conformational epitopes of the surface glycoprotein of caprine arthritis-encephalitis virus: Potential application to competitive-inhibition enzyme-linked immunosorbent assay for detecting antibodiesin goat sera

Four immunoglobulin G1 monoclonal antibodies (MAbs) to the gp135 surface en velope glycoprotein (SU) of the 79-63 isolate of caprine arthritis-encephal itis virus (CAEV), referred to as CAEV-63, were characterized and evaluated for their ability to compete with antibody from CAEV-infected goats. Three murine MAbs (MAbs GPB16A, 29A and 74A) and one caprine MAb (MAb F7-299) we re examined, All MAbs reacted in nitrocellulose dot blots with native CAEV- 63 SU purified by MAb F7-299 affinity chromatography, whereas none reacted with denatured and reduced SU, All MAbs reacted in Western blots with purif ied CAEV-63 SU or the SU component of whole-virus lysate following denatura tion in the absence of reducing agent, indicating that intramolecular disul fide bonding was essential for epitope integrity. Peptide-N-glycosidase F d igestion of SU abolished the reactivities of MAbs 74A and F7-299, whereas t reatment of SU with N-acetylneuraminate glycohydrolase (sialidase A) under nonreducing conditions enhanced the reactivities of all MAbs as well as pol yclonal goat sera, MAbs 29A and F7-299 were cross-reactive with the SU of a n independent strain of CAEV (CAEV-Co), By enzyme-linked immunosorbent assa y (ELISA), the reactivities of horseradish peroxidase (HRP)-conjugated MAbs 16A and 29A with homologous CAEV-63 SU were <10% of that of HRP-conjugated MAb 74A The reactivity of HRP-conjugated MAb 74A was blocked by sera from goats immunized with CAEV-63 SU or infected with CAEV-63, The reactivity of MAb 74A was also blocked by sera from goats infected with a CAEV-Co molecu lar clone, although MAb 74A did not react with CAEV-Co SU in Western blots. Thus, goats infected with either CAEV-63 or CAEV-Co make antibodies that i nhibit binding of MAb 74A to CAEV-63 SU, A competitive-inhibition ELISA bas ed on displacement of MAb 74A reactivity has potential applicability for th e serologic diagnosis of CAEV infection.