Antigens Flashcards
What does the Innate Immune System Recognize
a limited number of conserved PAMPs such as microbial nucleic acids or lipopolysaccharides in the bacterial cell wall
What can the adaptive immune system respond to?
almost all of the foreign macromolecules present in an invading microorganism
Antigens
substance specifically binds to antibodies or a cell surface receptor of B and T cells
Characteristics of Antigens
molecules that trigger adaptive immune responses. They are either large proteins, glycoproteins, or lipoproteins. Many different antigens can be found in a single microorganism.
Bacterial Antigens
Capsule (K antigens), Pili (F antigens), Flagellum (H antigens), Cell Wall (O antigens)
Bacterial Toxins
toxic proteins secreted by bacteria or released into the surrounding environment when they die. Toxins are highly immunogenic proteins and stimulate the production of antitoxins
Viral Antigens
nucleic acids, capsids, or matrix proteins
Where are viral antigens expressed?
on the surface of the host cells
Other microbial antigens
animals may be invaded by fungi, protozoan, parasites, arthropods, and helminths.
Non-microbial antigens
food, inhaled dust. Foreign molecules may be injected directly into the body through a snake or mosquito bite or by a veterinarian
Histocompatability Antigens
the cell surface proteins that trigger graft rejection
Autoimmune Responses
immune responses against normal body components
Autoantigens
antigens that induce autoimmunity. Can include hormones (thyroglobulin), structural components (basement membranes), complex lipids (myelin), intracellular components (mitochondrial proteins, nucleic acids, nucleoproteins), cell surface proteins (hormone receptors)
Tumor Antigens (Neoantigens)
produced as a result of tumor-specific mutation during the malignant transformation of normal cells
Superantigens
cause non-specific activation of T cells resulting in polyclonal T cell activation and massive cytokine release.
What produces superantigens?
pathogenic viruses and bacteria, as a defense mechanism against the immune system
Characteristics of good antigens
large, complex, stable, foreign
What make the best antigens?
foreign proteins
Carbohydrates
Simple polysaccharides are not good antigens because they are often degraded before the immune system has time to respond to them. More complex carbohydrates may be effective antigens, especially if bound to proteins
Lipids
poor antigens because of their wide distribution, relative simplicity, structural instability, and rapid metabolism. When linked to proteins or polysaccharides, they can trigger immune responses
Mammalian Nucleic Acids
poor antigens because of their relative simplicity and flexibility and because they are rapidly degraded
Microbial Nucleic Acids
have a different structure with many unmethylated CpG sequences. Can stimulate potent immune responses
Stainless Steel and Plastic
not antigens because they are inert and non-degradable.
What is the ability to stimulate an immune response determined by?
route of administration, amount of antigen administered, and genetic makeup of the immunized animal
Epitopes
prominent structural features on the surface of foreign molecules that are recognized by the immune system. Molecules will possess many different epitopes
Immunogens (complete antigens)
Antigens that are able to generate immune response by themselves. These are usually proteins, peptides, or polysaccharides with high molecular weight
Haptens (incomplete antigens)
antigens which are unable to generate the immune response themselves. Can be immunogenic if coupling with carrier proteins. Low molecular weight and non-protein substances
Carrier Molecule
non-antigenic component that helps in provoking the immune response
Cross-Reaction
Antigens directed against one antigen unexpectedly reacts with another apparently unrelated antigen. Results from the presence of shared epitopes on different antigens
Cross-Reaction Example
antisera to bovine serum albumin cross-react strongly with sheep and goat serum albumin but weakly with serum albumin from other mammals
How do superantigens bind non-specifically?
by cross-linking to the MHC and T cell receptor. This induces a signaling pathway that results in the proliferation of the cell and production of cytokines
