What age would you expect this man to be? (Patient with chronic lymphoblastic leukemia)

Correct Answer: C

Rationale: The correct answer is C (70+). Chronic lymphoblastic leukemia typically affects older adults, with the median age of diagnosis around 70 years old. This is due to the gradual accumulation of genetic mutations over time. Older patients are more likely to develop this type of leukemia compared to younger individuals. Choices A, B, and D are incorrect because they suggest younger age groups, which are less commonly associated with chronic lymphoblastic leukemia. Additionally, younger individuals are more likely to be affected by acute lymphoblastic leukemia rather than the chronic form.

Correct Answer: B

Rationale: The correct answer is B: immunoglobulin heavy-chain class. After binding to its specific antigen, a B lymphocyte can undergo class switching to change the type of antibody it produces while maintaining the same antigen specificity. This process involves recombination events that switch the constant region of the immunoglobulin heavy chain, leading to the production of antibodies with different effector functions. Choices A, C, and D are incorrect because they do not accurately describe the process of class switching in B lymphocytes. Light-chain isotypes, variable region of the heavy chain, and constant region of the light chain do not undergo class switching.

Correct Answer: A

Rationale: The correct answer is A: systemic anaphylaxis. When a child disturbs a wasp nest and is stung repeatedly, they can develop an allergic reaction leading to systemic anaphylaxis. This is a severe, rapid-onset allergic reaction that can cause shock due to widespread release of inflammatory mediators. Symptoms include difficulty breathing, swelling, low blood pressure, and can progress rapidly. Summary of other choices: B: Serum sickness is a delayed hypersensitivity reaction to foreign proteins, not typically seen in acute situations like this. C: An Arthus reaction is a localized immune complex-mediated hypersensitivity, not likely to result in systemic shock. D: Cytotoxic hypersensitivity involves antibodies attacking cells, not the rapid multi-system response seen in anaphylaxis.

Correct Answer: D

Rationale: The correct answer is D because toxic shock syndrome (TSS) is caused by superantigens, not A-B toxins. Superantigens directly activate a large number of T cells by binding to both the MHC class II protein and the T cell receptor simultaneously. This leads to massive cytokine release and the symptoms described. Choices A, B, and C are all accurate statements about the mechanism of action of superantigens in TSS. Choice D is incorrect because TSS toxins do not have an A-B subunit structure; they are superantigens that directly interact with T cells and do not enter cells to activate them.

Correct Answer: D

Rationale: The correct answer is D: enzymes released by polymorphonuclear cells. When immune complexes are deposited in the glomerular basement membrane, neutrophils (a type of polymorphonuclear cell) are recruited. These neutrophils release enzymes such as elastase and collagenase, which directly damage the membrane. Gamma interferon (choice A) is involved in immune response but does not directly damage the membrane. Phagocytosis (choice B) is the process of engulfing and digesting particles, not directly causing damage to the membrane. Cytotoxic T cells (choice C) target and kill infected or abnormal cells, but they are not directly involved in damaging the glomerular basement membrane in this scenario.