patogenantigen

A pathogen antigen is any molecule derived from a pathogenic organism that can be recognized by the immune system as foreign. These antigens are diverse and can be proteins, polysaccharides, lipids, or nucleic acids found on the surface or released by bacteria, viruses, parasites, or fungi. The specific portion recognized by immune receptors, an epitope, may be linear or conformational, and determines how strongly an antigen stimulates an immune response.

For recognition by the adaptive immune system, protein and some peptide antigens are processed and presented by antigen-presenting cells on major histocompatibility complex (MHC) molecules to T lymphocytes. B cells may recognize native antigens directly through their B cell receptors. Antigen presentation shapes the ensuing cellular and humoral responses, including antibody production and cytotoxic T cell activity. Pathogen antigens can be broadly conserved or highly variable, which influences immune detection and potential immune evasion through antigenic variation.

Antigens from pathogens are central to vaccination and diagnostic strategies. Vaccines often use selected pathogen antigens to elicit protective immunity without causing disease, sometimes enhanced with adjuvants. In diagnostics, tests may detect antibodies against specific pathogen antigens or the antigens themselves in patient samples.

Cross-reactivity, where antigens share epitopes with host proteins or other microbes, can complicate immune responses and diagnostics. Antigen structure, abundance, and exposure during infection all influence the strength and quality of the immune response to a pathogen. Examples include influenza hemagglutinin, SARS-CoV-2 spike protein, and bacterial surface polysaccharide antigens.