Which option correctly defines epitope spreading in immunology?

• A. Post-translational modifications to self-antigens.
• B. Modifications in gene expression that are not caused by changes in DNA sequence.
• C. Expansion of the immune response to unrelated antigens
• D. Cross-reaction with a pathogen similar self-antigen.

Answer: (C)

Epitope spreading describes how the immune response broadens from its initial target to additional epitopes over time. When an immune attack occurs against a specific epitope, inflammation and tissue damage can release other self-epitopes. Antigen-presenting cells then show these new epitopes to T and B cells, activating responses to new parts of the same protein or to different proteins altogether. Over time, the immune repertoire expands to recognize multiple epitopes, which helps explain the progression and worsening of autoimmune diseases. The idea here is the spreading to other (often unrelated) antigens, not just sticking to the original target. This is different from changes in gene expression without DNA changes, post-translational modifications, or pathogen-driven mimicry, which are separate immunological concepts.