Neutrophils: are a type of white blood cell that help your body fight infections, especially bacterial infections. They are an important part of your immune system. Normal neutrophil levels indicate your body has a healthy ability to fight infections. Low neutrophils (neutropenia) may increase your risk of infections and can be caused by certain medications, illnesses, or bone marrow problems. High neutrophils (neutrophilia) usually indicate infection, inflammation, stress, or other immune responses.