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Chapter 9. Immune System

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The epithelium that covers portions of the nonencapsulated lymphatic aggregates found along the gastrointestinal tract, such as tonsils and Peyer's patches, is functionally equivalent to which structure of a lymph node?

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A. Afferent lymphatic

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B. Cortex

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C. Efferent lymphatic

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D. Medullary cord

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E. Trabecula

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The answer is A: The epithelium of many nonencapsulated lymphatic aggregates serves to import antigens. In the case of Peyer's patches, microfold cells in the epithelium introduce antigens by transcytosis. Thus, the epithelium functions as afferent lymphatics for these structures.

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Deletions of part of chromosome 22 can produce a variety of developmental defects, such as DiGeorge syndrome, which may include the complete failure of the thymus to develop. What is the most likely effect on the adaptive immune system in children affected with this severe form of DiGeorge syndrome?

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A. B and T cells will be present in the blood and serum antibody levels will be normal

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B. B and T cells will be present in the blood and serum antibody levels will be reduced

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C. B cells will be present in the blood, serum antibody levels will be normal, and T cells will be absent

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D. B cells will be present in the blood, serum antibody levels will be reduced, and T cells will be absent

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The answer is D: B cells develop in bone marrow, thus naïve B cells will be produced and be present in the blood in the absence of the thymus. T cell development, however, requires the thymus for the first few decades of life, therefore T cells will be absent or severely depleted in the blood. The effective production of an antibody response by activated B cells requires Th cells, therefore serum antibody levels will be severely reduced due to the absence of T cells in this case.

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What is the principal reason that some lymphocytes are born with antigen receptors that recognize self-molecules?

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A. Antigen receptors must bind to self-major histocompatability complex molecules

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B. Clonal anergy requires self-reactive receptors

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C. Lymphocyte progenitor cells develop in central lymphoid tissue, which is a specialized, restricted environment

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D. Receptor genes are rearranged during cell development

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E. Self-reactive cells are required for immunologic surveillance

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