What is a key difference between innate and adaptive immunity?

Correct Answer: C

Rationale: Correct Answer: C Rationale: 1. Innate immunity is rapid: It provides immediate defense against pathogens. 2. Innate immunity is non-specific: It reacts in the same way to all pathogens. 3. Adaptive immunity, on the other hand, is slower and pathogen-specific. 4. Adaptive immunity develops memory to provide long-lasting protection. Summary: A: Innate immunity does not develop memory; adaptive immunity does. B: Adaptive immunity may not always be functional due to various factors. D: Adaptive immunity requires activation through exposure to specific antigens.

Correct Answer: B

Rationale: The correct answer is B: Alternative pathway. This pathway involves properdin, Factor B, and Factor D. Properdin stabilizes the C3 convertase complex formed by Factor B and Factor D, leading to the amplification of the complement cascade. The other choices are incorrect because: A: Classical pathway is initiated by antigen-antibody complexes binding to C1q. C: Lectin pathway is activated by lectins binding to carbohydrates on pathogen surfaces. D: Terminal pathway involves the formation of the membrane attack complex.

Correct Answer: C

Rationale: The correct answer is C: Autoimmune diseases such as SLE. C1q is essential for the classical pathway of the complement system, which plays a crucial role in clearing immune complexes. A deficiency in C1q can lead to impaired immune complex clearance, resulting in the development of autoimmune diseases like Systemic Lupus Erythematosus (SLE). Choice A (Enhanced inflammation) is incorrect because a deficiency in C1q would actually lead to decreased inflammation due to impaired complement activation. Choice B (Reduced phagocytosis) is incorrect because phagocytosis is primarily mediated by the alternative pathway of the complement system, not the classical pathway involving C1q. Choice D (Increased cancer risk) is incorrect as C1q deficiency is not directly associated with an increased risk of cancer.

Correct Answer: B

Rationale: The correct answer is B because clonal selection during lymphocyte activation leads to the formation of memory and effector cells. This process involves the proliferation and differentiation of the activated lymphocyte into these specialized cells, which play crucial roles in immune responses upon encountering the same antigen in the future. Cytokine suppression (choice A) is not the direct outcome of clonal selection but may be a regulatory mechanism during immune responses. Antigen elimination without cellular proliferation (choice C) is not accurate as clonal selection involves the expansion of specific lymphocyte clones. Destruction of the lymphocyte (choice D) is not the outcome of clonal selection, as activated lymphocytes undergo proliferation and differentiation rather than destruction.

Correct Answer: C

Rationale: The correct answer is C: IgG. IgG is the only antibody that can be transported across the placenta from the mother to the fetus, providing passive immunity to the newborn. This transfer of IgG occurs through the neonatal Fc receptor (FcRn) present in the placenta. IgA is primarily found in mucosal secretions, IgM is too large to cross the placenta, and IgE is involved in allergic reactions and parasitic infections, not placental transfer. Therefore, IgG is the only antibody capable of crossing the placenta and providing immune protection to the fetus.