Nokea
The immunoglobulin Joining chain (J-chain) is
- A. only produced by T-Cells
- B. only produced by neutrophils
- C. associated with only multimeric forms of IgM and IgA
- D. associated with IgE for histamine release
Correct Answer: C
Rationale: Step-by-step rationale:
1. The J-chain is a polypeptide involved in the formation of polymeric IgM and IgA.
2. Polymeric forms of IgM and IgA contain the J-chain, aiding in their multimeric structure.
3. The J-chain is not exclusive to T-cells or neutrophils, making choices A and B incorrect.
4. IgE is associated with FcεRI receptors for histamine release, so choice D is incorrect.
Summary:
The correct answer is C because the J-chain is specifically associated with the multimeric forms of IgM and IgA, helping to form their structure. Choices A, B, and D are incorrect as the J-chain is not solely produced by T-cells, neutrophils, or associated with IgE for histamine release.
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Which cells are the most important phagocytes in innate immunity?
- A. Natural killer cells and B lymphocytes
- B. Macrophages and neutrophils
- C. T cells and dendritic cells
- D. Basophils and eosinophils
Correct Answer: B
Rationale: The correct answer is B - Macrophages and neutrophils are the most important phagocytes in innate immunity. Macrophages are versatile cells that engulf and destroy pathogens, while neutrophils are the most abundant phagocytes in the blood and are critical for early immune responses. Natural killer cells and B lymphocytes (A) are not phagocytes, but rather involved in adaptive immunity. T cells and dendritic cells (C) play roles in adaptive immunity and antigen presentation, not direct phagocytosis. Basophils and eosinophils (D) are involved in allergic reactions and parasitic infections, not primary phagocytic functions.
Which complement protein is the main component of the Membrane Attack Complex (MAC)?
- A. C1
- B. C3
- C. C5b
- D. C4b
Correct Answer: C
Rationale: The correct answer is C: C5b. The Membrane Attack Complex (MAC) is formed by a sequence of complement proteins, with C5b playing a crucial role as the initiator. After C5b binds to the target cell membrane, it triggers the assembly of C6, C7, C8, and multiple C9 molecules to form the MAC pore. C1 (A) is the initiator of the classical pathway, not a component of the MAC. C3 (B) is involved in the formation of the C3 convertase and opsonization but is not the main component of the MAC. C4b (D) is part of the classical pathway and is involved in the formation of the C3 convertase, not the MAC.
What is the role of antibodies in adaptive immunity?
- A. Antigen presentation
- B. Pathogen destruction through phagocytosis
- C. Neutralization, opsonization, and complement activation
- D. Direct killing of infected cells
Correct Answer: C
Rationale: The correct answer is C: Neutralization, opsonization, and complement activation. Antibodies play a crucial role in adaptive immunity by neutralizing pathogens, facilitating their destruction through opsonization, and activating the complement system for pathogen elimination. This is achieved through binding to antigens on pathogens, marking them for destruction by phagocytes, and triggering the complement cascade. Options A, B, and D are incorrect because antibodies do not directly present antigens, perform phagocytosis, or kill infected cells.
One principal function of complement is to
- A. inactivate performs
- B. mediate the release of histamine
- C. Bind antibodies attached to cell surfaces and to lyse these cells
- D. phagocytize antigens
Correct Answer: C
Rationale: The correct answer is C because complement proteins bind antibodies attached to cell surfaces and cause cell lysis, enhancing immune response. Choice A is incorrect as complement does not inactivate performs. Choice B is incorrect as complement does not mediate the release of histamine. Choice D is incorrect as phagocytosis is a function of phagocytes, not complement proteins. Therefore, the correct function of complement is to enhance immune response by binding antibodies and causing cell lysis.
Which of the following is NOT a feature of T cells?
- A. They recognize three-dimensional structures of a pathogen
- B. Their receptors possess specificity
- C. Their receptors have one antigen-binding site
- D. Their antigen receptors are never secreted
Correct Answer: A
Rationale: The correct answer is A because T cells do not recognize three-dimensional structures of a pathogen. T cell receptors interact with processed antigen fragments presented by MHC molecules on antigen-presenting cells. Choice B is correct because T cell receptors possess specificity for antigens. Choice C is incorrect because T cell receptors have multiple antigen-binding sites. Choice D is incorrect as T cell receptors can be secreted as soluble forms.