I am stuck with these few 4 questions help would be really appreciated!!!

1. What is the name of the component(s) that allow white blood cells to recognize foreign invaders?

2. What is the role(s) of the Macrophage in the immune system?

3. What is the name of the component(s) that identify antigens of foreign invaders and signal response of the B-cells and killer T-cells?

4. What is the role(s) of the B-cell in the immune system?