Q5. A female presents with high grade fever, diffuse erythematous rash and hypotension. She is currently menstruating and using tampoons. The toxin responsible acts by?

1. A

   A. MHC class I molecule only

2. B

   B. CD4 receptor only

3. C

   C. B-cell receptor and IgG

4. D

   D. Vβ region of the T-cell receptor and MHC class II molecule

Appeared in: INI-CET EXAM -2026

Explanation

• The clinical presentation is characteristic of Toxic Shock Syndrome (TSS), caused by a bacterial superantigen.
• Superantigens cause disease by bypassing normal antigen presentation and directly cross-linking the Vβ region of the T-cell receptor (TCR) with an MHC class II molecule on an antigen-presenting cell.
• This non-specific binding triggers the activation of a large fraction of T-cells, leading to a massive release of cytokines (a 'cytokine storm').
• The cytokine storm is responsible for the systemic symptoms of TSS, including high fever, rash, and severe hypotension.

Why Other Options Were Wrong

• Option A: MHC class I molecules are involved in presenting intracellular antigens to CD8+ cytotoxic T-cells, a different pathway not utilized by TSS superantigens.
• Option B: The CD4 molecule is a co-receptor that helps stabilize the TCR-MHC class II interaction, but it is not the direct binding site for the superantigen toxin.
• Option C: B-cell receptors and IgG are components of the humoral immune system, responsible for antibody production. The acute phase of TSS is driven by a T-cell mediated cytokine storm, not an antibody response.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pathophysiology of Toxic Shock Syndrome (TSS) and the mechanism of superantigens as background academic context rather than a clinical decision trigger.
• Recognizing the triad of fever, rash, and hypotension in a menstruating woman using tampons is critical for early diagnosis of TSS, a life-threatening emergency.
• Immediate nursing actions include preparing for aggressive fluid resuscitation and antibiotic administration, and removing the source of infection (the tampon).
• Patient education on safe tampon use (e.g., using the lowest absorbency, frequent changes, alternating with pads) is a key nursing role in preventing TSS.

How to Approach the Question

• First, analyze the clinical vignette to identify the most likely diagnosis. The combination of high fever, rash, hypotension, and tampon use points strongly to Toxic Shock Syndrome (TSS).
• Recall the causative agent and pathophysiology of TSS. It is caused by exotoxins (superantigens) from bacteria like Staphylococcus aureus.
• The question asks for the mechanism of action of the toxin. Access your knowledge of immunology regarding how superantigens work.
• Evaluate each option based on the superantigen mechanism. A superantigen non-specifically links MHC class II molecules with T-cell receptors.
• Option D accurately describes this cross-linking of the Vβ region of the T-cell receptor and the MHC class II molecule.
• Eliminate the other options by identifying their roles in different immune pathways (MHC class I for intracellular pathogens, CD4 as a co-receptor, B-cells for humoral immunity).

Concept Tested & Keywords

• Concept Tested: Pathophysiology of Toxic Shock Syndrome (TSS) and the mechanism of superantigens.
• Stem keywords: high grade fever, diffuse erythematous rash, hypotension, menstruating, tampons
• Lead-in keywords: acts by
• Clinical cues: The combination of fever, rash, hypotension, and tampon use is a classic presentation for Toxic Shock Syndrome.

Question ID

QTCYowPraT-CPoeMxwnxzn

Copy ID

Reference Book

E6 Medicine Harrison 22e Part 1 pp. 1015-1017, 1034-1036

E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 354-356