Step 1: Understand the role of chemical messengers in immunity.
In the immune system, certain chemical messengers called cytokines regulate the activity of immune cells. These molecules help in communication between cells and activate different components of the immune response.
Step 2: Identify the messenger that activates NK cells and macrophages.
One important cytokine that activates Natural Killer (NK) cells and macrophages is Interferon-gamma (IFN-γ).
Step 3: Explain its function.
Interferon-gamma is produced mainly by activated T-lymphocytes and NK cells. It enhances the ability of macrophages to destroy pathogens and also stimulates NK cells to attack infected or abnormal cells.
Final Answer:
The chemical messenger that activates Natural Killer T-cells and macrophages is Interferon-gamma (IFN-γ).