Which of the following sentences is NOT true about type I hypersensitivity reactions?

Correct Answer: D

Rationale: Step 1: Type I hypersensitivity reactions are immediate allergic reactions that occur upon initial exposure to an allergen, not just after a second encounter. Step 2: Food allergies can lead to systemic anaphylaxis due to the rapid release of mediators like histamine. Step 3: TH2 lymphocytes play a crucial role in the development of type I hypersensitivity reactions by promoting IgE production. Step 4: Type I hypersensitivity reactions are not generally classified as genetic disorders since they result from an immune response to allergens, not a single gene defect.

Correct Answer: C

Rationale: The correct answer is C because OPV induces mucosal immunity that blocks enteric infection and viral transmission. This is crucial in preventing the spread of poliovirus through the fecal-oral route. Choice A is incorrect because OPV primarily induces an IgA response in the mucosal surfaces, not IgG. Choice B is incorrect because while OPV is effective, it carries a risk of vaccine-derived poliovirus, making IPV the preferred choice in some situations. Therefore, Choice C is the most accurate as it highlights the unique ability of OPV to induce mucosal immunity, which is essential for preventing poliovirus transmission.

Correct Answer: A

Rationale: The correct answer is A: How the number of different immunoglobulins produced by an individual can be far greater than the number of genes in the human genome. Immunoglobulin gene rearrangement occurs during B cell development, leading to the generation of a diverse repertoire of antibodies from a limited number of genes. This process allows for the production of a vast array of immunoglobulins through mechanisms like V(D)J recombination. Choice B is incorrect because the gene rearrangement process actually enables a single gene to encode for multiple immunoglobulins. Choice C is partially correct but does not fully capture the significance of gene rearrangement in expanding the diversity of immunoglobulins beyond what the genome would suggest. Choice D is incorrect as it combines a correct statement (A) with an incomplete statement (C).

Correct Answer: B

Rationale: The correct answer is B because polarizing cytokines secreted by dendritic cells play a crucial role in determining the differentiation of activated Th cells into specific effector subsets. These cytokines guide the Th cells towards different functional phenotypes, such as Th1, Th2, Th17, or Treg cells. This process helps tailor the immune response to the specific type of pathogen encountered. Choices A, C, and D are incorrect because while signal 1 of activation, T cell receptor co-receptors, and duration of signaling are important factors in T cell activation and differentiation, they do not have as direct and significant an impact on effector subset differentiation as the influence of polarizing cytokines.

Correct Answer: D

Rationale: The correct answer is D because all the factors mentioned are important in the eradication of smallpox. A is correct because smallpox is specific to humans, simplifying eradication efforts. B is correct as the vaccine was easily deployable. C is correct as isolation of symptomatic individuals helped control the spread. Therefore, all choices are important in the successful eradication of smallpox.