Which of the following are not typically found within secondary lymphoid tissues?

Correct Answer: B

Rationale: Correct Answer: B - Hematopoietic stem cells are not typically found within secondary lymphoid tissues because they are located in the bone marrow where they give rise to various blood cells. In contrast, secondary lymphoid tissues like lymph nodes and spleen primarily consist of mature immune cells and support immune responses. Naïve lymphocytes (A), dendritic cells (C), and antigens (D) are commonly found in secondary lymphoid tissues as they play crucial roles in the immune response.

Correct Answer: B

Rationale: Step 1: SCID is a genetic disorder affecting the immune system. Step 2: Inherited genetic mutations cause abnormalities in immune cells. Step 3: These mutations lead to severe deficiencies in immune function. Step 4: Choice B accurately reflects the genetic basis of SCID. Summary: Choice A is incorrect because SCID is not caused by HIV. Choice C is incorrect as it oversimplifies the immune deficiencies in SCID. Choice D is incorrect because SCID primarily affects immune cells, not stem cells.

Correct Answer: C

Rationale: Rationale: C is incorrect because naïve lymphocytes actually enter the lymph node through the afferent lymphatic vessel, not the efferent. A carries lymphocytes into the lymph node, and D is true since antigens enter through afferent vessels. B is correct, as naïve T cells are found in the paracortex.

Correct Answer: D

Rationale: The correct answer is D because neutralization by IgE along the mucosal surface of the gut is a major antibody-mediated mechanism against parasitic worms. IgE binds to antigens on the worm's surface, leading to the release of histamine and other mediators that help expel the worm. Neutrophil degranulation (A) is more associated with bacterial infections, opsonization (B) is mainly for phagocytosis of pathogens, and triggering physiological responses (C) is not a direct antibody-mediated defense against parasitic worms.

Correct Answer: C

Rationale: The correct answer is C because innate immune response is not mediated by lymphocytes. Innate response involves physical barriers, such as skin and mucous membranes, and cells like macrophages and neutrophils. Lymphocytes are part of the adaptive immune response, which is characterized by specificity and memory. Choice A is correct as the innate response acts rapidly due to pre-existing mechanisms. Choice B is correct as adaptive response results in memory cells for quicker response upon re-exposure. Choice D is correct as adaptive response can recognize and respond to specific pathogens through antigen recognition.