Alleged reaction in gel-immunodiffusion of an IgM monoclonal antibody with alfalfa mosaic virus and cucumber mosaic virus is an artefact

Researchers previously reported that an IgM monoclonal antibody (MAb 8) raised against alfalfa mosaic virus (AMV) cross-reacted with cucumber mosaic virus (CMV) in gel-immunodiffusion tests, suggesting a potential serological relationship between these two unrelated plant virus groups. This study investigated whether this cross-reactivity was genuine or artifactual. Using improved assay conditions, the authors demonstrated that MAb 8's reactions with both AMV and CMV disappeared when 0.1 M sodium chloride was incorporated into the gel, indicating non-specific binding rather than true antigenic cross-reactivity. Western blotting confirmed the non-specific nature of MAb 8, showing it reacted with multiple unrelated plant viruses when bovine serum albumin was used as blocking agent, but failed to react with any antigens when skimmed milk was used instead. Additionally, 45 polyclonal antisera collected from immunized animals showed no heterologous cross-reactivity between AMV and CMV under appropriate assay conditions. The authors conclude that the alleged serological relationship is an artifact resulting from unsatisfactory assay conditions rather than genuine antigenic similarity between these viruses.

Key findings

• MAb 8's cross-reactivity with AMV and CMV is abolished by incorporating 0.1 M-NaCI in gel-immunodiffusion, indicating non-specific binding
• The non-specific reactivity of MAb 8 is confirmed in Western blotting and eliminated when skimmed milk replaces bovine serum albumin as blocking agent
• Polyclonal antisera from AMV and CMV immunization show no heterologous cross-reactivity under appropriate assay conditions
• No serological relationship exists between AMV and CMV; their apparent cross-reactivity is an artifact of suboptimal assay conditions