What is made by white blood cells to help fight off infection?

What is made by white blood cells to help fight off infection? Antibody.

Antibodies are proteins produced by specialized white blood cells called B lymphocytes. When B cells recognize a foreign substance, such as a protein on a bacterium or virus, they can develop into plasma cells that release large quantities of antibodies into the blood and tissues.

Each antibody has a structure that allows it to bind to a particular antigen. This binding may block a virus from entering cells, mark bacteria for destruction, or help other immune cells identify the invader. Antibodies are part of adaptive immunity, which can remember earlier infections and respond more quickly the next time.

A common mix-up is calling antibodies themselves white blood cells: they are not cells, but immune proteins made by B-cell descendants. Vaccines work partly by training the immune system to produce antibodies without causing the targeted disease.