Antigens and Antibodies , Cell Receptors

1. AntigensandAntibodies,CellReceptors Maja Marković, 2nd year, 2013/2014 Mentor: A. Žmegač Horvat

2. Antigen • word origin: antibody generator / anti(body)-gen = any substance foreign to the body that evokes an immune response • parts of bacteria, viruses, parasites, foods, venoms, blood components, and cells and tissues of various species, including other humans

4. epitope - a molecular region on the surface of an antigen capable of eliciting an immune response and combining with a specific antibody

5. antigen ≠immunogen • hapten- a small molecule that can elicit an immune response only when attached to a large carrier such as a protein urushiol → quinone (reacts with skin proteins) hydralazine (blood pressure-lowering drug) → drug-induced lupuserythematosus halothane (anesthetic gas) → hepatitis penicillin-class drugs → autoimmune hemolytic anemia

6. allergens = antigens which produce an abnormally vigorous immune response to a perceived threat that would otherwise be harmless to the body

7. superantigens (SAg) • producedby pathogenic microbesas a defense mechanism against the immune system • cause non-specific activation of T-cells→ polyclonal T cell activation and massive cytokine release(interferon gamma → macrophages → proinflammarory cytokines IL-1, IL-6, TNF-alpha) •  antigen-induced T-cell response: 0.0001- 0.001% → 25 % •  shock and multiple organ failure

8. tumor antigens • presented by MHC I or MHC II molecules on the surface of tumor cells • tumor-specific antigens (TSAs) - presented onlyby tumor cells   • tumor-associated antigens (TAAs) - presented by tumor cells and normal cells • cytotoxic T lymphocytesmay be able to destroy tumor cells before they proliferate, B-cellsrecognizemutatedcellreceptors • used as tumor markers(alphafetoprotein, carcinoembryonic antigen CA-125, MUC-1, epithelial tumor antigen ) andvaccines

9. Antibodies • large glycoproteins, part of the immunoglobulin superfamily •  produced by plasma cells  • soluble or membrane-bound • basic structure: "Y"-shaped molecule two identical heavy chains(α, ε, γ, δ, and μ, define the class) two identical light chains(λ and κ)  connected by disulfide bonds constant and variable regions

10. Fab region- antigen-binding • paratope - at the amino terminal end of the antibody, variable domains from the heavy and light chains • FV region, variable loops of β-strands, three each on VL and VH • Fc region - ensures that each antibody generates an appropriate immune response for a given antigen (recognition of opsonized particles, lysis of cells, and degranulation of mast cells, basophils and eosinophils)

13. more than 350 typesofmoleculesmarkers on the cell surfacecriticalinantigen recognition (CD4, CD8)cell surface receptors for growth factors(CD135)

14. MHC molecules = major histocompatibility complex (human leukocyte antigen, HLA) • a set of cel-surface molecules encoded by a large gene family in all vertebrates • MHC-I: all nucleated cells; cytotoxic T lymphocyte • MHC-II: dendritic cells, mononuclear phagocytes,  B lymphocytes, some endothelial cells, epithelium of thymus; helper T lymphocytes

15. MHC determines compatibility of donors for organ transplant and one's susceptibility to an autoimmune disease via crossreacting immunization

16. Sources • Taradi, Milan: Imunologija, 7. dopunjeno izdanje, 2010. • http://www.merriam-webster.com/ • http://en.wikipedia.org/wiki/Antigen • http://en.wikipedia.org/wiki/Antibody