Transcript Antigens and Antibodies, Cell Receptors

Maja Marković, 2nd year,
2013/2014
Mentor: A. Žmegač Horvat
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
 epitope
- a molecular region on the surface of an
antigen capable of eliciting an immune response and
combining with a specific antibody
 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 lupus erythematosus
halothane (anesthetic gas) → hepatitis
penicillin-class drugs → autoimmune hemolytic anemia
 allergens
= antigens which produce an abnormally vigorous immune
response to a perceived threat that would
otherwise be harmless to the body
superantigens (SAg)
 produced by pathogenic microbes as 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
tumor antigens
 presented by MHC I or MHC II molecules on the surface
of tumor cells
 tumor-specific antigens (TSAs) - presented only by tumor
cells
 tumor-associated antigens (TAAs) - presented by tumor cells
and normal cells
 cytotoxic T lymphocytes may be able to destroy tumor cells
before they proliferate, B-cells recognize mutated cell receptors
 used as tumor markers (alphafetoprotein, carcinoembryonic
antigen CA-125, MUC-1, epithelial tumor antigen ) and
vaccines
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
 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)
more than 350 types of
molecules
markers on the cell surface
critical in antigen recognition
(CD4, CD8)
cell surface receptors for
growth factors (CD135)
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
 MHC determines compatibility of donors for organ
transplant and one's susceptibility to an autoimmune
disease via crossreacting immunization
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