There is a difference between pathogens and antigens, but the two are also closely related. Pathogens can refer to pathogenic microorganisms that invade the body and can refer to bacteria or viruses. When invading the body, for the immune system, it is not the pathogen that is seen, but some component of the antigen that is different from itself, and the immune system then produces antibodies against these antigens. A pathogen may appear to the immune system to be only one antigen, so that only one antibody is produced, or the immune system may split into many different antigens, which may produce many different antibodies. In other words, when a pathogen infects a person, it is possible to produce only one antibody, which is one set of antigen-antibody system, or it is possible to produce many antibodies, which is then multiple sets of antigen-antibody system. Some of these antibodies may be protective antibodies, while others may only be indicative of infection by this pathogen.