If the sample tested contained LMoV, the LMoV reacted with the IgG3 conjugated to colloidal gold. The colloidal gold-labeled IgG3–LMoV complex then migrated into the nitrocellulose membrane by means of capillary action and subsequently reacted with the immobilized IgG4 in the test line. Unbound colloidal gold-labeled IgG3 passed through the test line and reacted with the goat anti-rabbit IgG in the control line to form a second visible purple-red band.