Virology (Picornaviridae) — Within the picornavirus capsid (VP1, VP2, VP3, VP4), which structural protein is the major immunogenic component that elicits neutralizing antibodies (for example, in foot-and-mouth disease virus, the G–H loop)?

Introduction / Context:
Picornaviruses (such as foot-and-mouth disease virus, poliovirus, rhinoviruses) have icosahedral capsids made of four structural proteins: VP1, VP2, VP3, and VP4. Among these, VP1 is surface-exposed and carries key antigenic sites. Immunology and vaccinology questions often test recognition of which capsid protein induces neutralizing antibodies, because this underpins epitope-focused vaccine design and diagnostic serology.

Given Data / Assumptions:

• Picornavirus capsid is an icosahedral shell with repeating VP1–VP3 on the surface and VP4 on the inner face.
• Neutralizing epitopes must be accessible to antibodies.
• Foot-and-mouth disease virus (FMDV) VP1 contains an immunodominant G–H loop region.

Concept / Approach:
The most immunogenic and neutralization-relevant region must be solvent-exposed. VP1 is prominently displayed on the virion exterior. The famous G–H loop in VP1 (containing an RGD motif in FMDV serotypes) is a classic neutralization epitope. Therefore, VP1 is the best single choice for “immunogenic in nature.”

Step-by-Step Solution:

Verification / Alternative check:
Peptide vaccines and recombinant subunits targeting VP1 epitopes of FMDV elicit neutralizing antibodies; escape mutations frequently map to VP1 loop regions, confirming immunological pressure at VP1.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming any surface protein is equally immunogenic. Dominance depends on epitope exposure and flexibility; in picornaviruses, VP1 generally dominates neutralization.

Final Answer:
VP1.