## Core Concept
Cytokines are a large group of proteins, peptides, or glycoproteins that are secreted by specific cells of the immune system. They play a crucial role in the body's immune response, inflammation, and hematopoiesis by acting as signaling molecules. Cytokines can be classified into several types, including interleukins (IL), interferons (IFN), tumor necrosis factors (TNF), and chemokines, based on their functions and structures.

## Why the Correct Answer is Right
The correct answer, although not directly provided, requires an understanding of what is generally false regarding cytokines. Typically, cytokines are known for their roles in immune responses, including promoting or resolving inflammation, activating immune cells, and facilitating communication between different cell types. A statement that could be considered false might relate to their origin, function, or classification.

## Why Each Wrong Option is Incorrect
Without the specific details of options A, B, C, and D, we can still provide a general approach to evaluating why each option might be incorrect regarding cytokines:

- **Option A:** This option would be incorrect if it inaccurately describes a characteristic of cytokines that is actually true. For example, if it states that cytokines are primarily produced by immune cells, this would be a true statement, making it an incorrect choice if the question seeks a false statement.

- **Option B:** Similarly, if this option presents a false statement about cytokines that is actually known to be true, it would be incorrect. For instance, stating that cytokines only act locally would be false because while some cytokines act locally, others can act systemically.

- **Option C:** This would be incorrect if it suggests a function or characteristic of cytokines that is not accurate. For example, if it implies that cytokines are not involved in chronic inflammation, this would be false since cytokines play significant roles in both acute and chronic inflammatory processes.

- **Option D:** If this option presents a statement that is known to be true about cytokines, it would be an incorrect choice if the question asks for a false statement.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **cytokines are critical in the differentiation and function of T helper cells**, with different cytokines promoting the differentiation into Th1, Th2, Th17, or Treg cells, which have distinct roles in immune responses. This is a high-yield fact for exams as it connects basic immunology with clinical applications.

## Correct Answer: D.