A primary immune response in an adult human requires approximately how much time to produce detectable antibody levels in the blood?

Correct Answer: C

Rationale: The correct answer is C: 1 week. Firstly, after initial exposure to an antigen, it takes time for the immune system to recognize and mount a response. This is known as the lag phase. Next, B cells need to be activated, differentiate into plasma cells, and start producing antibodies. This process typically takes a few days. Finally, the antibodies need to reach detectable levels in the blood, which usually occurs around 1 week post-exposure. Choices A, B, and D are incorrect because 12 hours is too short for the immune response to fully develop, 3 days may be sufficient for antibody production but not yet detectable levels, and 3 weeks is longer than necessary for detectable levels to be reached in a primary immune response.

Correct Answer: B

Rationale: The correct answer is B: Individuals of blood group type AB are 'universal recipients' of transfusions. This is because individuals with blood type AB have both A and B antigens on their red blood cells, making them compatible with all blood types during transfusions. Choice A is incorrect because Rh factor is separate from ABO blood group system. Choice C is incorrect because individuals with blood type AB do not have circulating anti-A or anti-B antibodies. Choice D is incorrect because haplotype refers to a set of genes on one chromosome, which is not directly related to blood group type.

Correct Answer: B

Rationale: The correct answer is B because if DNA synthesis is not stimulated in the mixed-lymphocyte culture, it indicates that person Z has at least one allele that is different from person X's HLA-Dw7 allele. This rules out person Z being homozygous for HLA-Dw7 (choice A) as there would be no difference in HLA alleles between the two individuals. Similarly, person Z being heterozygous for HLA-Dw7 (choice C) is too specific as it assumes only one specific allele is different. Choice D is incorrect as it states that person Z does not carry the HLA-Dw7 allele, which cannot be concluded definitively from the information provided. Therefore, the most reasonable conclusion is that person Z is either homozygous or heterozygous for HLA-Dw7 (choice B) since there is a lack of DNA synthesis stimulation, indicating a difference in HLA alleles between the two individuals.

Correct Answer: B

Rationale: The correct answer is B: C3b. C3b is a key opsonin that binds to pathogens and enhances their recognition and ingestion by phagocytes. Macrophages and neutrophils have receptors for C3b, allowing them to efficiently phagocytose pathogens. Factor D, C6, and properdin are not directly involved in enhancing phagocytosis through opsonization. Factor D is part of the alternative pathway of complement activation, C6 is involved in forming the membrane attack complex, and properdin stabilizes the alternative pathway C3 convertase. Therefore, the presence of receptors for C3b on phagocytes is crucial for their ability to recognize and engulf pathogens effectively.

Correct Answer: C

Rationale: Rationale: C is incorrect because heavy-chain switching can occur in hybridoma cells, leading to the production of different antibody isotypes besides IgM. This process allows for the generation of antibodies with diverse functions. A, B, and D are correct: A: The spleen cell component provides the ability to form antibody as it contributes the B-cell's ability to produce antibodies. B: The myeloma cell component provides the ability to grow indefinitely due to its immortal nature. D: The antibody produced by a hybridoma cell is homogeneous and directed against a single epitope due to the clonal nature of hybridoma cells.