Which of the following is true of antigens?
Antigens are substances that activate the adaptive immune response.
Antigens are typically composed of nucleotides.
Antigens are produced by the body in response to a foreign invader.
Antigens are limited to one antigenic determinant per antigen molecule.
The Correct Answer is A
A. Antigens are substances that activate the adaptive immune response: Antigens are molecules, often proteins or polysaccharides, that are recognized as foreign by the immune system. Their presence triggers B and T lymphocytes to mount a specific adaptive immune response, including antibody production and cell-mediated immunity.
B. Antigens are typically composed of nucleotides: Antigens are usually composed of proteins, glycoproteins, or polysaccharides, not nucleotides. While nucleic acids can sometimes act as antigens, they are not the typical composition of antigenic substances.
C. Antigens are produced by the body in response to a foreign invader: Antigens themselves are foreign molecules or markers; they are not produced by the body. The body produces antibodies or immune cells that recognize and respond to antigens.
D. Antigens are limited to one antigenic determinant per antigen molecule: Many antigens have multiple antigenic determinants (epitopes), allowing them to be recognized by multiple antibodies or T cell receptors. They are not limited to a single determinant.
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Related Questions
Correct Answer is A
Explanation
A. Has a lag period while B cells proliferate and differentiate into plasma cells:The primary immune response involves initial exposure to an antigen. B cells require time to recognize the antigen, proliferate, and differentiate into plasma cells that secrete antibodies, resulting in a delayed but specific response.
B. Is another name for immunological memory:Immunological memory refers to the enhanced response of the secondary immune response due to memory cells. It is not synonymous with the primary immune response, which occurs upon first exposure to an antigen.
C. Occurs more rapidly and is stronger than the secondary response:The primary response is slower and weaker than the secondary response. Memory cells generated during the primary response enable the secondary response to act faster and with higher antibody production.
D. Occurs when memory cells are stimulated:Stimulation of memory cells triggers the secondary immune response, not the primary response. The primary response occurs when naive B and T cells encounter an antigen for the first time.
Correct Answer is A
Explanation
A. Antigenic:“Antigenic” is not a classification of T cells. It describes a property of a substance that can trigger an immune response, not a type of T lymphocyte.
B. Cytotoxic:Cytotoxic T cells (CD8+) directly kill infected or abnormal cells. They are a major type of T cell responsible for cell-mediated immunity and defense against viruses and cancer cells.
C. Regulatory:Regulatory T cells (Tregs) modulate the immune response by suppressing excessive or inappropriate activation. They help maintain immune tolerance and prevent autoimmune reactions.
D. Helper:Helper T cells (CD4+) assist other immune cells by releasing cytokines that stimulate B cells, cytotoxic T cells, and macrophages. They are essential for orchestrating the adaptive immune response.
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