Neutropenia - an explanation

I have been asked to explain what Neutropenia is.

Neutropenia is an abnormally low number of neutrophils in the blood.
Neutrophils serve as the major defense of the body against acute bacterial and certain fungal infections. Neutrophils usually constitute about 45% to 79% of all white blood cells in the bloodstream. When the neutrophil count falls below 1,000 cells per microliter of blood the risk of infection increases somewhat, when it falls below 500 cells per microliter, the risk of infection increases greatly. Without the key defense provided by neutrophils, a person has problems controlling infections and is then at great risk. The cause of Neutropenia developing happens when neutrophils are used up or destroyed in the bloodstream faster than the bone marrow can make new ones, for example in the case of certain cancers and the use of the very strong drugs, such as those used in chemotherapy. Still there are other reasons why the bone marrow shuts down - Aplastic Anemia is one. So to sum up, people who have severe neutropenia can rapidly succumb to infections because their bodies lack the means to fight invading organisms.

I am sure I will be corrected by the very many knowledgeable readers if this is wrong in some way, but this is my understanding of Neutropenia and I hope it helps in some way.