Which of the following statements about M cells is incorrect?

Correct Answer: D

Rationale: The correct answer is D because M cells do not transport IgA from the lamina propria into the intestinal lumen. Instead, they transport antigens and pathogens from the gut lumen to underlying immune cells. Choice A is correct as M cells are found in Peyer's patches. Choice B is correct as M cells are specialized epithelial cells. Choice C is incorrect as M cells have microfolds on their luminal side, not microvilli.

Correct Answer: B

Rationale: Correct Answer: B (VDJ gene rearrangement) Rationale: 1. VDJ gene rearrangement occurs during B cell development in the bone marrow, independent of T helper cells. 2. Somatic hypermutation and immunoglobulin class switching require T helper cell interactions. 3. Memory cell differentiation also involves T helper cells for activation and differentiation. 4. Therefore, VDJ gene rearrangement is the only process not directly dependent on antigen-specific T helper cells.

Correct Answer: A

Rationale: Neutrophils are typically not found in the lamina propria of the gut in the absence of infection because they are primarily involved in the acute inflammatory response to infections. Macrophages, plasma cells, and T cells are commonly present in the gut lamina propria to maintain immune homeostasis and respond to antigens. Neutrophils are more abundant in tissues during active infection due to their role in phagocytosis and inflammation. Therefore, the correct answer is A: Neutrophils.

Correct Answer: D

Rationale: The correct answer is D. By engineering a form of the antibody with human variable region protein sequences (choice B), it reduces the risk of immune response in patients. Similarly, by engineering a form with human constant region protein sequences (choice C), it further reduces immunogenicity. Therefore, both B and C contribute to making the antibody more suitable for human use, enhancing its efficacy and safety in treating neuroblastoma. Choices A and D are incorrect as they do not address the crucial aspect of reducing immunogenicity through humanization of the antibody.

Correct Answer: D

Rationale: Step-by-step rationale for why Answer D is correct: 1. Polyclonal antibodies are produced by multiple B cell clones in response to an antigen (Choice A). 2. These antibodies have varying affinities due to the diversity of B cell clones involved (Choice B). 3. Different antibody classes, such as IgM, IgG, IgA, etc., are produced by different B cells (Choice C). 4. Therefore, all options are correct as polyclonal antibodies exhibit these characteristics.