"Hamburger disease" is caused by

Correct Answer: C

Rationale: The correct answer is C: A strain of E. coli. "Hamburger disease" is commonly caused by E. coli O157:H7, a strain of Escherichia coli bacteria found in undercooked ground beef. This strain can lead to severe foodborne illness. Helicobacter pylori (Choice A) is associated with stomach ulcers, not hamburger disease. Salmonella typhimurium (Choice B) and Shigella flexneri (Choice D) are both known to cause food poisoning, but they are not typically linked to hamburger disease specifically. In this case, the unique association between E. coli O157:H7 and undercooked ground beef makes Choice C the correct answer.

Correct Answer: C

Rationale: Paul Ehrlich introduced the concept of discrimination between self and non-self through his "horror autotoxicus" theory. He proposed that the immune system can differentiate between harmful non-self antigens and self-antigens. Ehrlich's theory laid the foundation for understanding immune responses and the development of immunology. Metchnikoff focused on phagocytosis, Pasteur on microbiology, and Janeway on innate immunity, not specifically on self vs. non-self discrimination.

Correct Answer: B

Rationale: Neutrophils play a crucial role in the immune response by engulfing and destroying pathogens through a process called phagocytosis. This is essential for eliminating harmful invaders from the body. Neutrophils do not produce antibodies (choice A), activate lymphocytes (choice C), or synthesize cytokines (choice D), which are functions typically carried out by other immune cells like B cells and macrophages. Therefore, the correct answer is B as it directly aligns with the primary function of neutrophils in the immune response, which is to combat infections by destroying pathogens.

Correct Answer: C

Rationale: Pattern recognition in innate immunity, as proposed by Janeway, involves identifying common pathogen-associated molecular patterns (PAMPs). This is crucial for initiating the immune response against pathogens. PAMPs are specific molecular patterns found on pathogens but not on host cells. By recognizing these patterns, the innate immune system can quickly and effectively identify potential threats and trigger the appropriate immune response. Explanation of why other choices are incorrect: A: Specific recognition of antigens is a function of adaptive immunity, not innate immunity. B: Binding toxins to create immunity is not the primary role of pattern recognition in innate immunity. D: Suppressing lymphocyte activation is not the role of pattern recognition in innate immunity; rather, it is involved in activating immune responses against pathogens.

Correct Answer: C

Rationale: The main function of the Membrane Attack Complex (MAC) is to lyse pathogens by creating pores in their cell membranes. First, MAC assembles on the pathogen's surface. Then, it forms a pore, disrupting the pathogen's membrane integrity, leading to cell lysis. This mechanism is crucial for the immune system to effectively eliminate pathogens. Choice A (Recruitment of neutrophils) is incorrect because MAC is not involved in recruiting neutrophils. Neutrophil recruitment is typically mediated by other signaling molecules. Choice B (Phagocytosis activation) is incorrect as MAC does not directly activate phagocytosis. Phagocytosis is a separate process involving the engulfment of pathogens by immune cells. Choice D (Enhancing cytokine production) is incorrect because MAC does not directly enhance cytokine production. Cytokine production is mainly regulated by other immune cells and signaling pathways.