A 48-year-old man has had a chronic cough with fever for 3 months. On physical examination, his temperature is 37.9 degrees C. A chest radiograph reveals a diffuse bilateral reticulonodular pattern. A transbronchial biopsy is performed, and microscopic examination shows focal areas of inflammation containing epithelioid macrophages, Langerhans giant cells, and lymphocytes.

These findings are most typical for which type of immunologic response?

A. Type I
B. Type II
C. Type III
D. Type IV

The clinical condition of the 48-year-old man is indicative of a Type IV hypersensitivity reaction, a type of immune response that is primarily mediated by T cells. The inflammation containing epithelioid macrophages, Langerhans giant cells, and lymphocytes in the biopsy report are typical features of this response. The symptoms and radiograph findings also suggest chronic inflammation which is often associated with Type IV hypersensitivity.

Explanation:

The clinical information provided indicates that the 48-year-old man is showing a Type IV hypersensitivity reaction. This form of immune response, also known as delayed hypersensitivity, is primarily mediated by T cells, particularly CD4+ helper T cells and CD8+ cytotoxic T cells, rather than by antibodies.

In Type IV reactions, the antigen stimulates the production of sensitized T-cells, which then provoke an immune response. Focal areas of inflammation containing epithelioid macrophages, Langerhans giant cells, and lymphocytes, like those observed in the biopsy report, are hallmark features of a granulomatous reaction, a subtype of Type IV hypersensitivity.

This type of immune response is usually encountered in chronic infections or diseases like tuberculosis, sarcoidosis, and chronic asthma. The diffuse bilateral reticulonodular pattern seen in the chest radiograph also points towards chronic inflammation, commonly associated with Type IV hypersensitivity.

Learn more about Type IV hypersensitivity here:

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