Weekly Year 2: Cellular Immunology Exam - April 10, 2026 (Sections B & C) | Essay Questions | Ompath Study

Practice 7 structured short- and long-answer medical questions on Weekly Year 2: Cellular Immunology Exam - April 10, 2026 (Sections B & C). Review model ans...

Essay Questions and Answers

1. Q1. Describe the 'two-signal hypothesis' required for the activation of a naive T-cell, including the specific molecules involved in each signal.

   Answer: Signal 1 is the antigen-specific signal, mediated by the TCR-CD3 complex binding to the peptide-MHC complex on an APC. Signal 2 is the co-stimulatory signal, primarily the binding of CD28 on the T-cell to B7-1 (CD80) or B7-2 (CD86) on the APC. Without Signal 2, the T-cell enters a state of energy or apoptosis.

2. Q2. Outline the physiological role of the MHC Class I pathway and name the key intracellular components involved in peptide loading.

   Answer: The MHC Class I pathway presents endogenous antigens (e.g., viral or tumor proteins) to CD8+ T-cells. Key components include the Proteasome (degradation), TAP (transporter associated with antigen processing) into the ER, and the Tapasin/Chaperone complex (calnexin/calreticulin) for stable loading onto the MHC heavy chain.

3. Q3. Explain the mechanism by which Natural Killer (NK) cells distinguish between healthy host cells and virally infected or transformed cells.

   Answer: NK cells use a balance of activating and inhibitory receptors. Inhibitory receptors (e.g., KIRs) recognize MHC Class I molecules on healthy cells ('self'). If MHC Class I is downregulated (missing-self) or if activating ligands (e.g., MICA/B) are upregulated due to cellular stress, the inhibitory signal is lost/overpowered, triggering NK degranulation.

4. Q4. Describe the differentiation of Th1 and Th2 subsets, identifying the specific master transcription factor and primary effector cytokine for each.

   Answer: Th1 differentiation is driven by IL-12/IFN-gamma; its master transcription factor is T-bet, and its primary effector cytokine is IFN-gamma (cell-mediated immunity). Th2 differentiation is driven by IL-4; its master transcription factor is GATA-3, and its primary effector cytokine is IL-4, IL-5, or IL-13 (humoral/anti-helminth immunity).

5. Q5. Define 'central tolerance' in the context of T-cell development within the thymus.

   Answer: Central tolerance involves Positive Selection (ensuring T-cells recognize self-MHC) in the cortex and Negative Selection (eliminating T-cells with high affinity for self-antigen) in the medulla. This process, facilitated by AIRE expressing peripheral tissue antigens, prevents the exit of autoreactive T-cells into the periphery.

6. Q6. Briefly explain the role of the Inflammasome in the innate immune response and name one pro-inflammatory cytokine it activates.

   Answer: The inflammasome (e.g., NLRP3) is a multi-protein cytosolic complex that assembles in response to PAMPs or DAMPs. It activates the enzyme Caspase-1, which proteolytically cleaves pro-interleukins into their active forms. Key cytokines include IL-1beta or IL-18.

7. Q7. Compare and contrast the mechanisms of CD4+ T-cell and CD8+ T-cell effector functions. In your answer, include the recognition of antigen, the molecules released to execute their functions, and their roles in clearing specific types of pathogens.

   Answer: 1. Recognition: CD4+ recognize peptide on MHC Class II (Exogenous); CD8+ recognize peptide on MHC Class I (Endogenous). 2. Subsets/Execution: CD4+ differentiate into Th1, Th2, Th17, or Treg. They primarily function through cytokine secretion to 'help' other cells (e.g., IFN-gamma to activate macrophages, IL-4 for B-cell class switching). 3. CD8+ Execution: Primarily cytotoxic. They induce apoptosis in target cells via the Perforin/Granzyme pathway or Fas/FasL interaction. 4. Pathogen clearance: CD4+ are essential for orchestrating responses against extracellular bacteria, fungi, and parasites. CD8+ are essential for eliminating intracellular pathogens (viruses) and surveilling for malignant cells. 5. Coordination: CD4+ cells provide necessary IL-2 and licensing signals to APCs to optimize CD8+ memory and expansion.