ABSTRACT

The first stage of removing an invading organism is to recognize it as being foreign, that is, not “self” (Sections E and F). The immune system sees the invader as having a number of antigens. In the broad sense, an antigen is any substance which induces an immune response. Antigens recognized by cells of the innate immune system are called “pathogen-associated molecular patterns” (PAMPs) and initiate production of cytokines, chemokines, and antimicrobial peptides by these cells (Section B2). Recognition of antigens by lymphocytes results in proliferation and production of cytokines and/or antibodies. Antigens recognized by lymphocytes include proteins, carbohydrates, lipids, and nucleic acids. Responses can be made to virtually anything. Even self molecules or cells can act as antigens under appropriate conditions, although this is quite well regulated in normal healthy individuals (Section G).