What chemical in poison ivy is responsible for triggering contact dermatitis?

Correct Answer: B

Rationale: The correct answer is B: Urushiol oil. Urushiol oil is the allergen in poison ivy that triggers contact dermatitis. When urushiol oil comes into contact with the skin, it can cause an allergic reaction leading to redness, itching, and inflammation. Histamine (choice A) is a compound released by the body in response to allergens but is not the specific chemical in poison ivy. Lipopolysaccharide (LPS) (choice C) is a component of the outer membrane of certain bacteria and not present in poison ivy. C3a (choice D) is a complement protein involved in the immune response but not related to poison ivy dermatitis.

Correct Answer: E

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: The correct answer is B: During T cell differentiation, the decision to become a TH1 or a TH2 cell CD4+ is not a random event. This is because T cell differentiation into TH1 or TH2 cells is guided by specific signals from the environment, such as cytokines present during activation. TH1 cells are induced by IL-12 and IFN-gamma, while TH2 cells are induced by IL-4. This process is not random but rather a result of specific signaling cues. A: During T cell development, the decision to become a CD4 or a CD8 positive cell is not a random event. It is determined by interactions with thymic stromal cells and the T cell receptor. C: TH2 CD4+ cells do secrete IL-4, so this statement is true. D: IL-10 is not a TH2 polarizing cytokine; rather, it is known to have regulatory functions in immune responses.

Correct Answer: D

Rationale: The correct answer is D: CXCR4. CXCR4 is a chemokine receptor that serves as a co-receptor for HIV entry into target cells. Step 1: HIV binds to CD4 receptor on the target cell. Step 2: The viral envelope protein gp120 then interacts with either CXCR4 or CCR5 co-receptor to facilitate viral entry. Step 3: In the case of CXCR4-tropic HIV strains, CXCR4 is the co-receptor used for entry into the target cell. Therefore, choice D is correct. Choices A (gp120) and C (CR5) are incorrect as they are not co-receptors, while choice B (CR4) is not a known co-receptor for HIV entry.

Correct Answer: D

Rationale: The correct answer is D: Able to induce only a humoral response. Live attenuated vaccines can induce both humoral and cellular immune responses, not just humoral. This is because they mimic natural infection, leading to a broader immune response. A: Usually effective at a single dose - This is true for live attenuated vaccines, as they often provide long-lasting immunity with just one dose. B: Expensive handling and storage - Live attenuated vaccines can be more cost-effective due to fewer doses needed, not expensive. C: Potential hazard due to reversion to a virulent form - This is a concern with live attenuated vaccines, as there is a risk of the weakened virus reverting to a virulent form.