In response to a positive PPD skin test, which cell type predominates in the lesion analysis?

• A. B lymphocytes
• B. Cytotoxic T lymphocytes
• C. Eosinophils
• D. Macrophages

Answer: (D)

A positive PPD (purified protein derivative) skin test indicates a delayed-type hypersensitivity reaction, which is typically associated with an immune response to Mycobacterium tuberculosis or similar antigens. This response primarily involves a type of immune response known as cell-mediated immunity.

The predominant cell type that appears in the lesion analysis due to this response is macrophages. In the context of a PPD response, when the test is positive, the body recognizes the antigen presented in the skin and activates T lymphocytes, specifically CD4+ helper T cells. These activated T cells then produce cytokines that recruit and activate macrophages to the site of injection. The macrophages are crucial in the immune response, as they help to encapsulate and eliminate the foreign antigens.

In addition to macrophages, other immune cells may be present, such as T lymphocytes and, in some cases, eosinophils. However, the hallmark of the granulomatous response seen in a positive PPD test is the presence of activated macrophages, which can take on a multinucleated giant cell configuration and become epithelioid cells.

Therefore, in the context of a positive PPD skin test, macrophages play a central role in mediating and sustaining