The web sites of most schools list the faculty and their current research topics. It may be helpful to refer in your application to one or more specific faculty members whose research corresponds to your own research interests.
A bachelor's degree in immunology prepares you for many careers that require a four-year degree. However, it does not qualify you to design your own research projects or teach at the college level. You need an advanced degree for those jobs. With a bachelor's degree, you can work as a research assistant or in a supporting role in the immunology field.