Determinants of antigenicity Which factors primarily determine whether a substance will be antigenic (capable of eliciting an adaptive immune response)?

Introduction / Context:
Antigenicity depends on several properties of a molecule. Appreciating these determinants helps explain why some substances are highly immunogenic while others are poor antigens unless coupled to carriers (haptens). This knowledge informs vaccine design and diagnostic assay development.

Given Data / Assumptions:

• Molecules vary in chemical class (proteins, polysaccharides, lipids, nucleic acids).
• Physical factors like size and complexity influence immunogenicity.
• Host recognition of “non-self” is central to adaptive responses.

Concept / Approach:

Strong antigens are typically high-molecular-weight, complex proteins or polysaccharides with diverse epitopes. Small molecules (haptens) are not immunogenic unless conjugated to carriers. Foreignness (phylogenetic distance) increases likelihood of recognition; self molecules are usually tolerated. Chemical nature matters because proteins can be processed and presented effectively by MHC, eliciting T-dependent responses; polysaccharides often elicit T-independent responses with limited memory/class switching.

Step-by-Step Solution:

Verification / Alternative check:

Empirical vaccine performance (e.g., protein toxoids) and hapten-carrier experiments validate the roles of chemical nature, size, and foreignness in dictating immunogenicity.

Why Other Options Are Wrong:

• Choosing any single factor ignores multifactorial reality.
• “None” contradicts abundant immunological evidence.

Common Pitfalls:

• Equating antigenicity with immunogenicity in all contexts; doses, route, and adjuvants also matter.

Final Answer:

All of these