Here's why:

* Patrol the body: White blood cells circulate throughout the body in the bloodstream and lymphatic system.

* Seek out invaders: They have specialized receptors that allow them to recognize and target foreign invaders like bacteria, viruses, and parasites.

* Destroy bacteria: Different types of white blood cells have different mechanisms for destroying bacteria. Some engulf and digest them (phagocytosis), while others release chemicals that kill them.

* Aid in immunity: White blood cells are a crucial part of the immune system. They work together to identify, attack, and eliminate pathogens, preventing infections and protecting the body.

Let me know if you have any other questions!