In tuberculosis, the cytokine playing major role in the conversion of tissue macrophages in to epithelloid cells –
**Core Concept**
Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis, which primarily affects the lungs. In the pathogenesis of TB, the conversion of tissue macrophages into epithelioid cells is a crucial step, contributing to granuloma formation and containment of the infection.
**Why the Correct Answer is Right**
The cytokine responsible for this conversion is interferon-gamma (IFN-γ), produced by T helper 1 (Th1) cells. IFN-γ activates macrophages, leading to the expression of major histocompatibility complex (MHC) class II molecules and the production of tumor necrosis factor-alpha (TNF-α). This results in the transformation of macrophages into epithelioid cells, which eventually fuse to form multinucleated giant cells. The granulomatous reaction formed by epithelioid cells and giant cells helps to isolate the bacteria and prevent their spread.
**Why Each Wrong Option is Incorrect**
**Option A:** TNF-α is involved in the formation of granulomas but is not the primary cytokine responsible for the conversion of macrophages into epithelioid cells.
**Option B:** Interleukin-12 (IL-12) is a cytokine that promotes the differentiation of Th1 cells, which then produce IFN-γ, but it is not directly involved in the conversion of macrophages.
**Option C:** Interleukin-4 (IL-4) is a cytokine that promotes the differentiation of Th2 cells, which are involved in humoral immunity and are not directly involved in the conversion of macrophages into epithelioid cells.
**Clinical Pearl / High-Yield Fact**
The granulomatous reaction in TB is characterized by the presence of epithelioid cells, giant cells, and a central area of necrosis. The containment of M. tuberculosis by granulomas is a hallmark of the body's immune response to this infection.
**Correct Answer:** C. Interferon-gamma (IFN-γ)