Lens protein of eye is an example of:

NHM MP Staff Nurse-2022

Microbiology

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Appeared in: NHM MP Staff Nurse-2022

Explanation

Sequestered antigens are self-antigens that are anatomically isolated from the immune system during embryonic development.
The lens of the eye is an immunologically privileged site, meaning its internal proteins are not normally exposed to circulating immune cells.
Because tolerance is not developed against these 'hidden' proteins, their subsequent exposure due to trauma or surgery can lead to an autoimmune response.
This phenomenon is responsible for conditions like sympathetic ophthalmia, where an injury to one eye leads to an immune attack on both eyes.

Option A: Neoantigens are newly formed antigens that the body has not previously encountered. They typically arise from genetic mutations (e.g., in cancer cells) or modifications by chemicals or viruses. Lens protein is a normal, pre-existing self-protein, not a newly created one.
Option C: Cross-reacting antigens involve 'molecular mimicry,' where a foreign antigen (like from a bacterium) is so similar to a self-antigen that an immune response against the foreign invader also attacks the body's own tissues. Lens protein is a self-antigen, not a foreign one that mimics self.
Option D: Forbidden clones are not a type of antigen but a theoretical concept in autoimmunity. The theory suggests that autoimmune diseases arise when self-reactive T or B cell clones, which should have been destroyed (deleted) during immune system development, manage to survive and later become activated.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Types of antigens and mechanisms of autoimmunity as background academic context rather than a clinical decision trigger.
Understanding sequestered antigens is crucial for nurses managing patients with penetrating eye injuries. There is a risk of sympathetic ophthalmia, a rare but devastating autoimmune condition where an injury to one eye triggers inflammation in the uninjured eye.
Nurses must educate patients on the importance of reporting any vision changes, pain, or redness in either eye following trauma to one eye.
What if? If a patient undergoes cataract surgery, the lens capsule is intentionally opened. While rare, this can also expose lens proteins and lead to a localized autoimmune inflammatory reaction known as phacoanaphylactic endophthalmitis, reinforcing the concept of lens protein as a sequestered antigen.

How to Approach the Question

First, identify the core concept of the question, which is the classification of antigens in immunology.
Read the stem carefully: 'Lens protein of eye'. This points to a specific self-protein in a unique location.
Recall the definitions of the four options provided: Neoantigen (new), Sequestered antigen (hidden), Cross-reacting antigen (mimicry), and Forbidden Clones (theory).
Consider the anatomy of the eye. The lens is known to be an 'immunologically privileged' site, meaning it's isolated from the main immune system.
Connect this anatomical fact with the definitions. The term 'sequestered' means isolated or hidden away, which perfectly describes the status of lens proteins.
Eliminate the other options based on their definitions. Lens protein isn't new (ruling out neoantigen), it isn't a foreign mimic (ruling out cross-reaction), and 'forbidden clones' is a theory about cells, not a type of antigen.

Concept Tested & Keywords

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E6 Microbiology Applied AnjuDhir 3e Part 2 p. 92-94

E6 Microbiology Essentials Sastry 4e Part 1 p. 142-144