A patient skin-tested with purified protein derivative (PPD)... develops induration at the skin test site 48 hours later. Histologically, the reaction site would MOST probably show

Correct Answer: C

Rationale: The correct answer is C because the purified protein derivative (PPD) is used to test for tuberculosis, which elicits a delayed-type hypersensitivity reaction. Helper T cells and macrophages are key players in this response, as they release cytokines and activate macrophages to combat the antigen. Eosinophils (A) are more commonly seen in allergic reactions, neutrophils (B) are prominent in acute bacterial infections, and B cells (D) are involved in antibody production, not the primary response to PPD.

Correct Answer: D

Rationale: Rationale for Correct Answer (D): Haptens are small molecules that can bind to antibodies without inducing an immune response on their own. They require a carrier protein to become immunogenic and induce an antibody response. However, haptens do not need to be processed by CD8+ cells to become immunogenic, as they primarily induce responses from B cells. CD8+ cells are involved in processing antigens for presentation to T cells. Therefore, statement D is incorrect. Summary of Incorrect Choices: A: True - haptens can bind to antibodies. B: True - haptens require a carrier protein to induce antibody response. C: True - both penicillin and poison ivy allergens are haptens.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Active immunity is when the body produces its antibodies after being exposed to a specific pathogen. 2. When someone has chicken pox, their immune system creates memory cells that recognize the virus. 3. If exposed to the virus again, the memory cells quickly respond, preventing re-infection. 4. This demonstrates active immunity as the individual's immune system actively defends against the pathogen. Summary: A: Biological control does not apply as it refers to natural predators controlling pest populations. B: Negative feedback is a regulatory mechanism in the body, not related to immunity. D: Passive immunity involves receiving pre-formed antibodies, not the body's own immune response like in the case of chicken pox.

Correct Answer: D

Rationale: The correct answer is D because the human immunodeficiency virus (HIV) attacks and weakens the immune system, making the body unable to defend itself against pathogens and cancerous cells. HIV specifically targets CD4 T cells, crucial for coordinating immune responses. This leads to a compromised immune system, leaving the body vulnerable to infections and unable to combat cancerous cells effectively. Choice A is incorrect as a genetic tendency toward diabetes does not directly impact the body's ability to defend against pathogens and cancerous cells. Choice B is incorrect as ringworm is a fungal infection that can be treated and does not typically affect the immune system in a way that compromises defense mechanisms. Choice C is incorrect as the production of antibodies in response to an infection is a normal immune response that helps the body fight off pathogens, rather than weakening the immune system.

Correct Answer: B

Rationale: The correct answer is B because bringing the sexual partner in for treatment is a key aspect of preventing the spread of genital warts. By ensuring that the partner is screened and treated, it helps to prevent reinfection and further transmission. Choice A is incorrect as resuming sexual activity before the lesions are healed can lead to the spread of infection. Choice C is incorrect because condom use should continue even after treatment to prevent the transmission of STIs. Choice D is incorrect as proper hygiene, including washing the affected area, is important in managing genital warts and preventing complications.