**Core Concept**
Chemotaxis is the movement of cells, particularly leukocytes, towards or away from chemical signals. It plays a crucial role in immune responses, inflammation, and the homing of stem cells to specific tissues. In the context of chemotaxis, various chemical signals, including chemoattractants and chemorepellents, can influence the movement of cells.

**Why the Correct Answer is Right**
Chemotaxis is promoted by chemoattractants, which are molecules that bind to specific receptors on the surface of cells, triggering a signaling cascade that ultimately leads to cell movement. For example, the binding of C5a to its receptor on neutrophils triggers a signaling pathway that increases the intracellular concentration of calcium, leading to the activation of actin polymerization and cell movement. In contrast, chemorepellents, such as C3a and Factor Xa, can also regulate chemotaxis, but they typically inhibit or reduce cell movement.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we cannot address it.
**Option B:** This option is not provided, so we cannot address it.
**Option C:** This option is not provided, so we cannot address it.
**Option D:** This option is not provided, so we cannot address it.

**Clinical Pearl / High-Yield Fact**
Chemotaxis is a critical component of the immune response, particularly in the recruitment of leukocytes to sites of inflammation. Understanding the molecular mechanisms underlying chemotaxis can provide insights into the development of novel therapeutic strategies for the treatment of inflammatory diseases.

**Correct Answer:**
(Note: Please provide the correct options A, B, C, and D for a complete explanation.)