Antigen vs. Pathogen

Main Difference

The main difference between antigen and pathogen is that antigen is a protein whereas a pathogen is a disease-causing agent.

Difference Between Antigen and Pathogen

Comparison Chart

Antigen vs. Pathogen

An antigen is an agent that generates the antibody. It is not an organism but a molecule attached to an external organism that activates an antibody response. It triggers the response of different antibodies depending on its match. While a pathogen is any foreign particle which is not part of the body, invades the body mainly in the bloodstream. It can also be something which produces harms to the body and affects the normal functioning of the body.

Antigens are the proteins, polysaccharides, lipids and nucleic acids whereas pathogens are organisms that are made of a bunch of components but in the end, they are also made of proteins, carbohydrates, and lipids. An antigen can be of exogenous antigen, endogenous antigen, autoantigen or neoantigen. These types are based on the presence of antigen inside or on the body or mechanism of action whereas a pathogen can be bacteria, virus, protozoa, fungi or parasites. These types cause different diseases in the body through different mechanisms.

What is Antigen?

An antigen is any substance that is characterized by the body as a foreign particle and starts an immune response. The antigen can be protein, lipid, polysaccharide or nucleic acid. An antigen determinant or epitope is the part of an antigen that attaches to the antibody. An antibody which is also known as an immunoglobulin is a glycoprotein produced in response to a specific antigen. The antibody is produced by the plasma cells in the blood after identifying a foreign substance or particle in the body. The four types of antigens are exogenous antigen, endogenous antigen, autoantigen, and neoantigen. The exogenous antigen is present on the surface of the microorganism that invades the body for example bacteria, virus, pollens, etc. The endogenous antigen is the metabolic product of the pathogen produced inside the body such as blood group antigens, histocompatibility leukocyte antigen, etc. The autoantigen is the molecule or cell in the body which is mistakenly known as non-self by the immune system such as single peptide vaccine insulin. This type of recognition can cause autoimmune disease, destroying self-tissues and organs in the body. The neoantigen is the molecule expressed on the surface of the cells infected by an oncogenic virus.

The antigen can also be classified into two types based upon the ability of an antigen to carry out their functions; complete antigen and incomplete antigen (hapten). A complete antigen can induce antibody formation and produce a particular and observable reaction with the antibody so produced. The incomplete antigen is a substance which is capable of producing antibody formation by themselves but after combing with large molecules.

What is Pathogen?

A pathogen is an agent which causes ailment or disease in the host. The pathogen can be microorganisms such as virus, bacteria, fungi, algae, protozoa, and parasite. Microorganisms can be present on or in the human body. These microorganisms usually do not cause any harmful effects. They are called natural flora. The natural flora lives either on the skin, in the mouth, vagina or intestine. These organisms are the cause of some benefits. However, there is another type of microorganism which can cause illness and diseases to the host. They are called pathogens. Typically, the pathogen is recognized by the immune system of the host’s body by identifying various antigens on the surface of the pathogens. The recognition of a foreign antigen initiates an immune response which destroys the pathogen. Antibodies are synthesized in the body in response to a particular pathogen, and these antibodies attach to the specific antigens to neutralize it. When antibodies bind with the pathogens, they may either immobilize the pathogen or kill the pathogens by letting it be recognized by phagocytic cells in the immune system. The pathogen can also be engulfed through complement reactions by attaching complement proteins to the pathogens. Also, some pathogens have developed specialized procedures for the survival and multiplication inside the host’s body. They can avoid the host’s innate and adaptive immune responses. The sign and symptoms of a disease can arise either by the pathogen or the reaction of the host’s body which must be healed.

Conclusion

The conclusion of this discussion is that both antigen and pathogen are immunogens that trigger immune’s response in hosts. Antigen is a protein present on the surface of a pathogen whereas pathogen is a disease causing agent.