<em>Antigens</em> are proteins that are found on the surface of a pathogen and <em>white blood cells </em>(leukocytes) are the cells of the immune system which helps fight infection and protect the body from foreign antigens.
Whenever a foreign antigen enters the body, a type of white blood cell called as the lymphocyte recognizes it and then produces antibodies against it, to generate an immune response.
So, <em>an immune response is primarily due to white blood cells recognizing foreign antigens.</em>
