Which of the following is an example of an immune stimulant herb?

Elder, specifically elderberry (Sambucus nigra), is recognized as an immune stimulant herb. It has been widely studied for its ability to enhance immune function, particularly in combating respiratory infections and influenza. Elderberry contains antioxidants, such as flavonoids, which can help strengthen the body's immune response by promoting the production of immune cells and providing antiviral properties. Its traditional use during the cold and flu season highlights its reputation as an herb that supports immune health.

Ginger, turmeric, and cayenne, while possessing beneficial health properties, primarily fall into different categories. Ginger is known for its anti-inflammatory and digestive benefits; turmeric is celebrated for its anti-inflammatory and antioxidant properties largely due to curcumin; and cayenne is noted for its circulation-boosting and metabolic-enhancing qualities through capsaicin. While all these herbs can support health in various ways, elderberry specifically serves as an immune stimulant, making it the best choice in this context.