Graft and tumor rejection are mediated primarily by

Correct Answer: D

Rationale: The correct answer is D: cytotoxic T cells. Cytotoxic T cells play a crucial role in graft and tumor rejection by directly targeting and killing foreign or abnormal cells. They recognize antigens presented on the surface of these cells and release cytotoxic molecules to destroy them. Non-complement-fixing antibodies (A) are involved in opsonization and neutralization but not the primary mediators of graft and tumor rejection. Phagocytic cells (B) such as macrophages can help in clearing cellular debris but are not as directly involved in targeting and destroying specific foreign or abnormal cells. Helper T cells (C) play a role in coordinating immune responses but are not the primary effectors in graft and tumor rejection.

Correct Answer: A

Rationale: The correct answer is A. Class II MHC proteins are found on the surface of antigen-presenting cells such as macrophages, dendritic cells, and B cells, but not on T cells. They play a crucial role in presenting antigens to T cells. Choice B is correct as Class II MHC proteins exhibit high polymorphism, contributing to immune diversity. Choice C is correct as they are indeed involved in antigen presentation by macrophages. Choice D is correct as Class II MHC proteins have a binding site for CD4 proteins on helper T cells, facilitating antigen recognition. Therefore, the incorrect statement among the choices is A, as Class II MHC proteins are not found on the surface of T cells.

Correct Answer: A

Rationale: The correct answer is A: antigens. Antigens are molecules that can trigger an immune response in the body. Certain microbes, foreign tissues, and cancerous cells all contain antigens that are recognized as foreign by the immune system, leading to an immune response. Choice B: enzymes, Choice C: fats, and Choice D: cytoplasm do not have the ability to trigger immune responses like antigens do. Enzymes are proteins that catalyze biochemical reactions, fats are molecules used for energy storage, and cytoplasm is a component of cells but none of them are recognized by the immune system as foreign invaders.

Correct Answer: B

Rationale: The correct answer is B: Increased mucus secretion- histamine release; neurotransmitter the body produces during an allergic reaction. Histamine release during an allergic reaction triggers the production of mucus to protect the airways from allergens. This increased mucus secretion helps to expel the allergen and reduce inflammation in the airways. Choices A, C, and D are incorrect because histamine does not cause bronchial dilation (A), decreased heart rate (C), or skin dryness and flaking (D) during an allergic reaction.

Correct Answer: B

Rationale: The correct answer is B because erythema at the incision site is an early sign of a wound infection. It indicates inflammation and possible bacterial presence, necessitating nurse intervention. WBC count within range (choice A) does not necessarily rule out infection. Clear drainage (choice C) may not always indicate infection, and reduced pain (choice D) can be subjective and not a reliable indicator of infection. Erythema is a specific indicator that warrants immediate attention to prevent further complications.