- The immune system attacks bacteria once they have invaded the body
- Bacteria is a kind of pathogen sometimes
- Therefore, the immune system attacks pathogens in the body

- The immune system attacks pathogens in the body
- White blood cells are a part of the immune system
- Therefore, white blood cell attacks pathogens in the body

- White blood cell attacks pathogens in the body
- Pathogens can cause disease
- Therefore, white blood cells attack disease in the body

So, white blood cells attack disease in the body
Question: What is a job of white blood cells?
Context: - The immune system attacks bacteria once they have invaded the body 
- White blood cells are a part of the immune system 
- Pathogens can cause disease 
- Bacteria is a kind of pathogen sometimes