T cells help B cells to:

Correct Answer: D

Rationale: The correct answer is D, "All of the above." T cells help B cells undergo isotype switching by providing cytokines. They also help B cells produce antibodies against protein antigens by activating them. T cells provide signal 2 of activation to B cells through the interaction of CD40 on B cells with CD40L on T cells. Therefore, all of these functions are critical for the collaboration between T and B cells in the immune response.

Correct Answer: B

Rationale: The correct answer is B because Ehrlich proposed that each cell producing antibodies would express several receptors, each specific for different antigens, whereas Burnet proposed that each single antibody-producing cell expresses only one type of receptor. This is the main difference between the two theories. Ehrlich's concept of multiple receptors per cell allows for a broader range of specificity and diversity in the immune response. The other choices are incorrect because they do not directly address the main difference between the two theories as outlined above. Choice A is incorrect because both Ehrlich and Burnet emphasized the importance of specificity, but they differed in their views on receptor diversity per cell. Choice C is incorrect because it focuses on the identity of soluble antibodies and receptors, which is not the main differentiator between the two theories. Choice D is incorrect as it mentions the release of soluble antigen receptors, which is not the main point of differentiation between Ehrlich and Burnet's theories.

Correct Answer: C

Rationale: The correct answer is C: ROS (Reactive Oxygen Species) is not a PAMP (Pathogen-Associated Molecular Pattern) because it is not a specific molecular pattern derived from pathogens. PAMPs are recognized by the innate immune system to trigger an immune response. Viral dsRNA, peptidoglycan, and flagellin are all examples of PAMPs as they are specific molecules commonly found in pathogens that can be recognized by pattern recognition receptors (PRRs) on immune cells, leading to activation of the immune response.ROS, on the other hand, are reactive molecules produced by host cells in response to pathogens but are not specific molecular patterns derived from pathogens. Therefore, ROS is not considered a PAMP.

Correct Answer: B

Rationale: Step 1: Acute-phase proteins are a group of proteins produced by the liver in response to inflammation or infection. Step 2: Mannose binding lectin (MBL) is an acute-phase protein that plays a role in the innate immune response. Step 3: MBL binds to pathogens and activates the complement system to enhance immune responses. Step 4: Selectins are cell adhesion molecules, not acute-phase proteins. Step 5: Lysozyme is an enzyme that destroys bacterial cell walls, not typically classified as an acute-phase protein. Step 6: Defensins are antimicrobial peptides, not typically classified as acute-phase proteins. Summary: MBL is the correct choice as it is a well-known acute-phase protein involved in the immune response. Selectins, Lysozyme, and Defensins are not typically classified as acute-phase proteins and are involved in different functions.

Correct Answer: A

Rationale: The correct answer is A: IgM. During a primary immune response, IgM antibodies are the first class produced by plasma cells. IgM is the largest antibody and is effective at agglutinating pathogens. It is later followed by IgG production. IgE is involved in allergic reactions and parasitic infections, not typically produced in large amounts during a primary response. IgA is more abundant in mucosal tissues and secretions.