During a viral infection, a 23-year-old female develops enlarged lymph nodes at multiple sites (lymphadenopathy). A biopsy from one of these enlarged lymph nodes reveals a proliferation of reactive T immunoblasts, cells that have prominent nucleoli. These reactive T cells are most likely to be found in which one of the following regions of the lymph node?
Correct Answer: Paracoex
Description: Lymph nodes may be enlarged (lymphadenopathy) secondary to reactive processes, which can be either acute or chronic. Acute reaction (acute nonspecific lymphadenitis) can result in focal or generalized lymphadenopathy. Focal lymph node enlargement is usually the result of bacterial infection. Sections from involved lymph nodes reveal infiltration by neutrophils. In contrast, generalized acute lymphadenopathy is usually the result of viral infections and usually produces a proliferation of reactive T lymphocytes called T immunoblasts. These reactive T cells tend to have prominent nucleoli and can be easily mistaken for malignant lymphocytes or malignant Hodgkin cells. Reactive processes involving lymph nodes typically involve different and specific poions of the lymph nodes depending upon the type of cell that is reacting. For example, reactive B lymphocytes typically result in hyperplasia of the lymphoid follicles and germinal centers (follicular hyperplasia). Examples of diseases that are associated with follicular hyperplasia include chronic inflammation caused by organisms, rheumatoid ahritis, and AIDS. Lymph nodes from patients with AIDS undergo characteristic changes that begin with follicular hyperplasia with loss of mantle zones, intrafollicular hemorrhage ("follicle lysis"), and monocytoid B cell proliferation. Subsequently there is depletion of lymphocytes (CD4+ lymphocytes) in both the follicles and the interfollicular areas. In contrast to reactive B cell processes, reactive T lymphocytes typically result in hyperplasia involving the T cell areas of the lymph node, namely the interfollicular regions and the paracoex. Examples of clinical situations associated with a T lymphocyte response include viral infections, vaccinations, use of some drugs (paicularly Dilantin), and systemic lupus erythematosus. The sinusoidal pattern of reaction involves expansion of the sinuses by benign macrophages, as seen in reactive proliferations of the mononuclearphagocytic system. Stellate microabscesses (irregular areas composed of central necrotic cellular and neutrophil debris surrounded by palisading macrophages) are characteristic of cat-scratch disease, lymphogranuloma venereum, and tularemia Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition.
Category:
Pathology
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