Chemically-induced tumors have tumor-associated transplantation antigens that

Correct Answer: B

Rationale: The correct answer is B because tumor-associated transplantation antigens can vary between different tumors of different histologic types even if induced by the same carcinogen. This is due to the fact that different histologic types of tumors can express different antigens, leading to variations in the transplantation antigens. Choice A is incorrect because tumor-associated transplantation antigens can differ even with the same carcinogen. Choice C is incorrect because the strength of the antigens is not specified in the question. Choice D is incorrect as tumor-associated transplantation antigens can indeed induce an immune response.

Correct Answer: D

Rationale: The correct answer is D because in the determination of serum insulin levels by radioimmunoassay, we need isotope-labeled insulin (choice A) as a tracer for detection, anti-insulin antibody made in goats (choice B) to bind to insulin, and anti-goat gamma globulin made in rabbits (choice C) to detect the antibody bound to insulin. Isotope-labeled anti-insulin antibody made in goats (choice D) is not needed as it is not typically used in this assay. This choice would not contribute to the accurate measurement of serum insulin levels.

Correct Answer: B

Rationale: The correct answer is B: carcinoembryonic antigen (CEA). CEA is elevated in patients with progressive colon carcinoma and in normal fetuses. This is because CEA is produced during fetal development and is also present in certain cancers. It is not a viral antigen (A), as CEA is a protein produced by cells. Alpha-fetoprotein (C) is elevated in certain liver conditions and cancers, but not specifically in colon carcinoma. Heterophil (D) is a type of antibody produced in response to infection, not related to CEA levels in colon carcinoma.

Correct Answer: C

Rationale: The correct answer is C because the alternative complement pathway can be initiated independently of C3b fragments. It is activated by foreign surfaces directly, such as certain bacteria or viruses, without the need for prior activation of C3b. This is a key feature that distinguishes the alternative pathway from the classical pathway. Choices A, B, and D are incorrect because A is true - the alternative pathway can be triggered by infectious agents in the absence of antibodies, B is true - it does not require C1, C2, or C4, and D is false - the alternative pathway has a different terminal sequence of events compared to the classic pathway.

Correct Answer: A

Rationale: The correct answer is A: Streptococcal antigens induce antibodies cross-reactive with heart tissue. This is known as molecular mimicry, where antibodies produced against the streptococcal antigens also react with antigens present in heart tissue, leading to carditis. This mechanism is the basis for the development of rheumatic heart disease following a streptococcal infection. Choice B is incorrect because it does not explain the specific relationship between streptococcal infection and carditis. Choice C is incorrect as it describes a mechanism related to IgE and histamine release, which is not the primary mechanism involved in carditis. Choice D is incorrect as it focuses on neutrophils and proteases, which are not the primary mediators of carditis in the context of a streptococcal infection.