Which scientist is credited with identifying Toll-like receptors (TLRs) in innate immunity?

Correct Answer: B

Rationale: The correct answer is B: Jules Hoffman. He is credited with identifying Toll-like receptors (TLRs) in innate immunity. Hoffman's research provided crucial insights into how the immune system recognizes pathogens and triggers immune responses. Paul Ehrlich is known for his work on antibodies, Edward Jenner for developing the smallpox vaccine, and Louis Pasteur for his contributions to germ theory and vaccination. However, none of them are specifically associated with the discovery of Toll-like receptors in innate immunity.

Correct Answer: C

Rationale: The correct answer is C: Lymphoid lineage. NK cells are a type of lymphocyte that is part of the innate immune system. They are derived from common lymphoid progenitors in the bone marrow. NK cells play a crucial role in recognizing and killing infected or abnormal cells. Myeloid lineage (A) gives rise to cells like macrophages and granulocytes, not NK cells. Erythroid lineage (B) produces red blood cells, and granulocyte lineage (D) gives rise to neutrophils, basophils, and eosinophils, not NK cells. Therefore, the correct choice is C as NK cells originate from the lymphoid lineage.

Correct Answer: A

Rationale: The correct answer is A: Lysosomes. Lysosomes contain enzymes that break down engulfed pathogens during phagocytosis. First, the pathogen is engulfed by the cell membrane forming a phagosome. Next, the phagosome fuses with a lysosome forming a phagolysosome where digestion occurs. Golgi apparatus (B) is involved in protein processing and packaging. Endoplasmic reticulum (C) is responsible for protein synthesis and lipid metabolism. Mitochondria (D) produce energy in the form of ATP.

Correct Answer: C

Rationale: The correct answer is C: Streptococcus pneumoniae infections. Complement deficiencies impair the body's ability to fight bacterial infections, particularly encapsulated bacteria like Streptococcus pneumoniae. Asthma (A), SLE (B), and chronic hepatitis (D) are not directly associated with increased susceptibility to bacterial infections due to complement deficiencies. Asthma is a chronic respiratory condition, SLE is an autoimmune disease, and chronic hepatitis affects the liver. Therefore, only Streptococcus pneumoniae infections are directly linked to complement deficiencies.

Correct Answer: B

Rationale: The correct answer is B: Macfarlane Burnet. Burnet proposed the concept of clonal selection in the 1950s to explain how the immune system recognizes and responds to specific antigens. He suggested that lymphocytes with receptors specific to antigens undergo clonal expansion upon encountering the antigen. This hypothesis laid the groundwork for our understanding of adaptive immunity. A: Paul Ehrlich developed the side-chain theory of antibody formation, not clonal selection. C: Louis Pasteur is known for his work in microbiology and vaccination, not clonal selection. D: Elie Metchnikoff is credited with discovering phagocytosis, not clonal selection.