The role of the B lymphocytes is to produce antibodies against antigens, which leads to the destruction of the pathogen.
Antibodies are Y-shaped protein molecules which have binding sites specific to particular antigens. When antibodies bind to antigens, the pathogen is inactivated.
B lymphocytes can trigger an immune response against substances that are harmless to the body, for example, pollen. This can trigger conditions such as hay fever and allergic asthma. This hypersensitive response to a harmless antigen is called an allergic reaction.