The Virus-Like Particles Capture Assay: A Method to Isolate Antigen-Displaying VLPs from a Sample Using Neutralizing Antibody-Conjugated Magnetic Beads

Neutralizing antibodies, or NAbs, are secreted by cells to protect them against invading viruses.

To study the interactions of NAbs with viruses, use engineered virus-like particles, or VLPs. These nanosized structures contain an assembly of virus-derived proteins without viral genetic material, making them non-infectious. VLPs are surrounded by a lipid bilayer embedded with antigenic envelope glycoproteins, which present a neutralizing epitope, a specialized region to which the NAbs bind.

Add the VLPs to a tube containing neutralizing antibodies bound to protein-conjugated magnetic beads. Incubate under agitation to prevent the beads from settling down. During incubation, the epitope region of the VLPs recognizes the complementary paratope on the Fab region of the NAbs, resulting in antigen-antibody complexes. This, in turn, helps the magnetic beads to capture the VLPs.

Place the tube in a separation rack equipped with a strong magnet. Under the influence of a magnetic field, the beads complexed with VLPs move toward the magnet without disturbing the antigen-antibody interaction. This step captures the bound VLPs, while the ones lacking specific antigens remain in the supernatant.

Discard the supernatant, and wash the pellet with washing buffer to remove unbound VLPs. Resuspend the VLP-bead complexes in an elution buffer, which causes the VLPs to disengage from the beads and appear in the supernatant.

Aspirate the isolated antigen-displaying VLPs into a fresh tube, and store them under refrigeration for further analysis.