What is the role of class II MHC proteins on donor cells in graft rejection?

Correct Answer: B

Rationale: The correct answer is B because class II MHC proteins on donor cells are recognized by helper T cells, leading to the activation of cytotoxic T cells which then kill the donor cells. This process is crucial in graft rejection as it triggers an immune response against the foreign cells. Choice A is incorrect because class II MHC proteins are not receptors for interleukin-2. Choice C is incorrect as class II MHC proteins do not induce the production of blocking antibodies. Choice D is incorrect because class II MHC proteins do not induce IgE production, which is involved in allergic reactions, not graft rejection.

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: C

Rationale: Rationale for Correct Answer (C): When spleen cells from a donor mouse are injected into a genetically dissimilar recipient mouse, it can lead to a graft-versus-host reaction. This is because the recipient's immune system recognizes the donor cells as foreign and mounts an immune response against them. In this case, since the donor mouse is of strain A and the recipient is an F1 hybrid of strains A and B, the genetic disparity is significant, leading to a higher likelihood of a strong immune response from the recipient against the donor spleen cells. Summary of Incorrect Choices: A: The spleen cells being destroyed is less likely as the recipient's immune system would typically recognize and respond to foreign cells rather than simply destroy them. B: Spleen cells surviving without any effect is unlikely because of the genetic disparity between the donor and recipient mice. D: Inducing tolerance of strain A grafts in the recipient is less likely as a strong immune response is expected due to the genetic differences between

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.