An immunologist is a biomedical scientist who specializes in the study of the immune system. The immune system is responsible for defending our bodies against diseases and infections, so an immunologist's work involves understanding how it functions, what triggers it to respond, and how it can be harnessed to fight various illnesses. Immunologists may study the human body's natural defense mechanisms or develop vaccines and therapies for specific diseases. They often work in research labs, universities, hospitals, pharmaceutical companies, or government agencies.