**Core Concept**
Epithelioid cells are a type of modified macrophage that plays a crucial role in the granulomatous response, particularly in tuberculosis. They are characterized by their large size, abundant cytoplasm, and often, a horseshoe-shaped nucleus. In the context of tuberculosis, epithelioid cells are formed from the fusion of activated macrophages.

**Why the Correct Answer is Right**
Epithelioid cells are primarily secretory cells that produce a variety of substances, including enzymes, cytokines, and chemokines. These secretions contribute to the formation of the granuloma and are essential for limiting the spread of Mycobacterium tuberculosis. The secretory function of epithelioid cells involves the production of granulysin, a protein that has been shown to have antimicrobial activity against M. tuberculosis. Additionally, epithelioid cells secrete pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1β), which help to recruit other immune cells to the site of infection.

**Why Each Wrong Option is Incorrect**
**Option A:** Phagocytosis is a function of macrophages, but not the primary function of epithelioid cells. While epithelioid cells may exhibit some phagocytic activity, their secretory function is more critical in the context of tuberculosis.

**Option C:** Antigenic refers to the ability of a substance to stimulate an immune response. While epithelioid cells may present antigens to T-cells, their primary function is not antigenic.

**Option D:** Healing is a broader process that involves the resolution of inflammation and tissue repair. While epithelioid cells contribute to the formation of the granuloma, their primary function is not directly related to the healing process.

**Clinical Pearl / High-Yield Fact**
The formation of epithelioid cells from activated macrophages is a key feature of the granulomatous response in tuberculosis. This process is facilitated by the presence of interferon-gamma (IFN-γ), which is secreted by T-cells.

**✓ Correct Answer: B. Secretory. Epithelioid cells are primarily secretory cells that produce a variety of substances to limit the spread of M. tuberculosis.**