When was the first vaccine for smallpox developed?

Correct Answer: B

Rationale: The correct answer is B: 1796. This is because the first vaccine for smallpox was developed by Edward Jenner in 1796. He used cowpox virus to create immunity against smallpox. Choices A, C, and D are incorrect because they do not align with historical records of the development of the smallpox vaccine. Choice A (1726) is too early, choices C (1882) and D (1895) are much later dates and do not correspond to the actual timeline of the smallpox vaccine's discovery.

Correct Answer: D

Rationale: The correct answer is D. Innate immunity does not involve producing antigen-specific antibodies. This is because innate immunity is the first line of defense against pathogens and does not have the ability to produce antibodies that target specific antigens. Instead, innate immunity works through mechanisms like phagocytosis and killing infected cells to eliminate pathogens. Choices A, B, and C are functions of innate immunity. A - Killing virally infected cells is a common function of innate immunity. B - Phagocytosis is the process by which immune cells engulf and destroy pathogens, a key function of innate immunity. C - Activating adaptive immunity is also a role of innate immunity, as it helps initiate the adaptive immune response for a more targeted defense.

Correct Answer: C

Rationale: Rationale: 1. Deficiencies in the classical pathway lead to impaired clearance of immune complexes, hence contributing to SLE. 2. This pathway plays a crucial role in removing self-antigens and maintaining immune tolerance. 3. Increased cancer risk (A) is not directly linked to classical pathway deficiencies. 4. Resistance to bacterial infections (B) is more associated with deficiencies in the alternative pathway. 5. Overactivation of adaptive immunity (D) is not a direct consequence of classical pathway deficiencies.

Correct Answer: B

Rationale: The correct answer is B: C3b acts as an opsonin to enhance phagocytosis. C3b binds to pathogens and enhances their recognition by phagocytic cells, facilitating their engulfment and destruction. This process is crucial for efficient immune responses. A, MAC formation, is initiated by the membrane attack complex, not C3b. C, inflammation, is triggered by various mediators such as histamine and cytokines, not C3b. D, neutralizing cytokines, is not a function of C3b; cytokines are regulatory proteins involved in immune responses.

Correct Answer: B

Rationale: The main limitation of innate immunity compared to adaptive immunity is that innate immunity lacks memory and specificity. This means that innate immune responses do not improve upon repeated exposure to the same pathogen and cannot target specific antigens efficiently. Adaptive immunity, on the other hand, can remember previous encounters with pathogens and mount targeted responses. Choices A, C, and D are incorrect because innate immunity can produce cytokines, includes physical barriers like skin and mucous membranes, and can activate complement as part of its defense mechanisms.