Which of the following statements is incorrect about celiac disease?

Correct Answer: C

Rationale: The correct answer is C because celiac disease primarily involves an abnormal adaptive immune response to gluten, not an innate response. Here's the rationale: 1) Celiac disease is characterized by a T-cell mediated response to gluten peptides in genetically susceptible individuals. 2) The adaptive immune system, particularly T cells, plays a crucial role in the pathogenesis by recognizing gluten peptides presented by HLA-DQ2 or HLA-DQ8 molecules. 3) This adaptive immune response leads to inflammation and damage to the intestinal mucosa. 4) In contrast, the innate immune system may also be activated, but it is not the primary driver of the disease. Summary: A: Correct - There is a strong genetic association with HLA alleles. B: Incorrect - Celiac disease is primarily driven by an adaptive immune response, not just features of autoimmunity. D: Incorrect - While gluten exposure triggers the immune response, the disease is not solely driven by gluten intake.

Correct Answer: B

Rationale: Step 1: Secondary lymphoid tissues bring together antigen-presenting cells and lymphocytes, facilitating the activation of naïve lymphocytes. Step 2: Co-localization of these components is essential for efficient immune response initiation. Step 3: Maturation and expression of antigen receptors primarily occur in primary lymphoid tissues, not secondary. Summary: A: Incorrect. Maturation of lymphocytes occurs mainly in primary lymphoid tissues. C: Incorrect. Contact with self-antigens is necessary for self-tolerance and occurs in primary lymphoid tissues. D: Incorrect. Only choice B accurately describes the critical role of secondary lymphoid tissues.

Correct Answer: D

Rationale: Thymocytes undergoing positive selection express both CD4 and CD8 co-receptors along with a functional T-cell receptor (TCR). CD4 and CD8 help in recognizing MHC molecules, while TCR is crucial for antigen recognition. Positive selection ensures that thymocytes with a functional TCR that can interact with self-MHC molecules survive. Therefore, the correct answer is D, as thymocytes undergoing positive selection express TCR, CD4, and CD8. Choice A, TCR alone, is incorrect as CD4 and CD8 are also expressed. Choices B and C are incorrect as positive selection involves the expression of both CD4 and CD8, not just one or the other.

Correct Answer: A

Rationale: Negative selection is the correct answer because it refers to the process that eliminates developing T cells with high affinity for self-peptide/MHC complexes to prevent autoimmune reactions. During negative selection, T cells that bind too strongly to self-antigens are deleted or rendered functionally inactive. This ensures that only T cells with moderate affinity for self-antigens are allowed to mature and participate in immune responses. Summary of other choices: B: Positive selection involves the selection of T cells that can recognize self-peptide/MHC complexes, promoting their maturation and survival. C: Peripheral tolerance refers to mechanisms that maintain self-tolerance in the mature immune system, not specifically related to eliminating self-reactive T cells during development. D: Lineage commitment is the process by which precursor cells differentiate into specific immune cell types and is not directly related to eliminating self-reactive T cells.

Correct Answer: A

Rationale: Step-by-step rationale: 1. In severe Covid-19 cases, there is usually a dysregulated immune response. 2. Type I Interferon plays a crucial role in early antiviral defense. 3. However, in severe cases, there is often a blunted or delayed response of type I Interferon. 4. This delayed response contributes to viral persistence and hyperinflammation. 5. Therefore, the prompt and sustained production of type I Interferon is not usually observed in severe Covid-19 cases. Summary: - Choice A is correct as the prompt and sustained production of type I Interferon is not typically observed in severe Covid-19 cases. - Choices B, C, and D are incorrect as autoantibodies, a delayed CD4 T cell response, and elevated levels of inflammatory cytokines are commonly observed in severe Covid-19 cases.