A child disturbs a wasp nest, is stung repeatedly, and goes into shock within minutes... This is MOST likely to be due to

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: 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.

Correct Answer: C

Rationale: The correct answer is C because complement lyses cells by forming a membrane attack complex (MAC) which involves the insertion of complement proteins into the cell membrane, leading to cell lysis. Choices A, B, and D are incorrect as complement does not lyse cells through enzymatic digestion, activation of adenylate cyclase, or inhibition of elongation factor 2. Complement-mediated lysis specifically involves the formation of MAC to disrupt the target cell membrane.

Correct Answer: D

Rationale: The correct answer is D because in autoimmune hemolytic anemia, activation of the complement system leads to the formation of membrane attack complexes (MAC) that directly lyse the red blood cells. This process is known as complement-mediated hemolysis. Perforins from cytotoxic T cells (Choice A) are involved in cell-mediated cytotoxicity but are not typically responsible for hemolysis of red blood cells. Neutrophils releasing proteases (Choice B) or interleukin-2 binding to its receptor on red cells (Choice C) are not mechanisms commonly associated with hemolysis in autoimmune hemolytic anemia.

Correct Answer: A

Rationale: The correct answer is A: They have the same amino acid sequence. This statement is incorrect because the variable regions of heavy chains and light chains in an antibody molecule have different amino acid sequences. The variable regions are responsible for binding to specific antigens, making choice B correct. The heavy and light chains are encoded by different genes on the same chromosome, making choice C incorrect. Both heavy and light chains contain hypervariable regions that contribute to antigen binding specificity, making choice D correct. Overall, the variable regions of heavy and light chains have distinct amino acid sequences, contributing to the diversity and specificity of antibodies.