What would you expect to see on a bone marrow biopsy? (For the man in Q9)

Correct Answer: B

Rationale: The correct answer is B: Auer rods. A bone marrow biopsy in a patient with leukemia may show Auer rods, which are needle-shaped cytoplasmic inclusions found in myeloid cells. Auer rods are characteristic of acute myeloid leukemia. Smudge cells (choice A) are seen in chronic lymphocytic leukemia. Reed-Sternberg cells (choice C) are found in Hodgkin's lymphoma. Lytic lesions (choice D) are seen in multiple myeloma, but are not typically identified on a bone marrow biopsy. Thus, Auer rods are the most likely finding on a bone marrow biopsy in a patient with leukemia.

Correct Answer: A

Rationale: The correct answer is A because C3b is not involved in altering vascular permeability. C3b plays a role in promoting phagocytosis by opsonizing pathogens, forming alternative-pathway C3 convertase for amplifying the complement cascade, and forming C5 convertase to initiate the terminal pathway. In contrast, altering vascular permeability is primarily mediated by other factors such as histamine and bradykinin. Therefore, C3b's involvement in altering vascular permeability is not supported by the functions it actually performs in the complement system.

Correct Answer: C

Rationale: The correct answer is C: a cell-mediated response. Poison ivy and poison oak reactions are primarily caused by contact with urushiol, an oil found in these plants. This oil triggers a cell-mediated immune response, involving T cells. T cells release cytokines that lead to inflammation and the characteristic rash. IgG and IgE responses are mainly involved in antibody-mediated immune responses, not in poison ivy reactions. Arthus reaction is a localized immune complex-mediated hypersensitivity reaction, not typically associated with poison ivy or poison oak.

Correct Answer: D

Rationale: The correct answer is D: indirect fluorescent-antibody test. This method is the best for demonstrating IgG on the glomerular basement membrane in kidney tissue. It involves applying a fluorescent-tagged anti-IgG antibody, which specifically binds to IgG on the tissue section, producing a visible fluorescent signal under a microscope. This technique allows for precise localization and visualization of IgG deposition. A: precipitin test and C: agglutination test are not suitable for detecting IgG specifically on tissue sections. B: complement fixation test is not commonly used for direct visualization of IgG in tissues. The indirect fluorescent-antibody test is the most sensitive and specific method for detecting IgG in tissue samples.

Correct Answer: D

Rationale: The correct answer is D because the statement is false. Antigens do not preselect V and J segments for gene recombination. Instead, the process is random. V, D, and J segments do combine to encode the antigen-binding site, making choice C true. Choice A is true because there are many V region segments available for gene recombination. Choice B is also true as there are several J segments and several D segments available for recombination. Therefore, the correct answer is D because it inaccurately describes the process of gene segment recombination.