## Core Concept
Chemotactic factors are substances that direct the movement of cells, particularly immune cells like neutrophils and macrophages, toward a specific location. This process is crucial in the inflammatory response and in fighting infections. Chemotactic factors can include a variety of molecules such as leukotrienes, complement components, and cytokines.

## Why the Correct Answer is Right
The correct answer, Leukotriene B4 (LTB4), is a well-known chemotactic factor. It is a product of arachidonic acid metabolism through the lipoxygenase pathway. LTB4 attracts neutrophils, eosinophils, and other leukocytes to sites of inflammation, making it a key player in the initiation and amplification of inflammatory responses.

## Why Each Wrong Option is Incorrect
- **Option A:** While certain components of the complement system, such as C5a, are indeed chemotactic factors, the option is not specified. However, assuming it's not C5a, we can consider it incorrect based on the specificity of the correct answer.
- **Option B:** This option is not specified, but if it's not a recognized chemotactic factor like LTB4, it would be incorrect.
- **Option D:** Similarly, without specification, if this option does not accurately represent a known chemotactic factor, it would be incorrect.

## Clinical Pearl / High-Yield Fact
A key point to remember is that chemotactic factors are critical in the recruitment of immune cells to sites of infection or inflammation. Leukotriene B4 (LTB4) is particularly notable for its role in attracting neutrophils and is involved in conditions such as asthma and rheumatoid arthritis.

## Correct Answer: C. Leukotriene B4