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Any foreign substance
Any foreign substance that is capable of inducing an immune response.
Are immunogens antigens?
All immunogens are antigens but not all antigens are immunogens.
Characteristics of non-immunogenic antigens
- <100,000 daltons (smaller)
- Chemical composition of nucleic acids and lipids.
Characteristics of immunogenic antigens
- > 100,000 daltons (larger)
- Chemical composition of proteins and polysaccharides
Complexity of Immunogens
Stimulate the production of autoantibodies.
Stimulate the production of alloantibodies.
The key portion of the immunogen against which the immune response is directed; Antigenic determinant site.
- Low molecular weight antigen
- Non-immunogenic by itself
- Immunogenic only when bound to a carrier molecule
Antigens that belong to the host
Antigens from other members of the host species.
Antigens which are either identical or closely related in structure to the specific antigen that antibody to one will cross-react with antibody.
A substance administered with a immunogen that enhances and potetiates the immune response.
Functions of Adjuvants
- Prolongs existence of immunogen in an area
- Increases effective size of immunogen
- Increases # of macrophages involved in antigen processing.
Factors that influence the Immune Response
- Route of inoculation
- health status
- genetic predisposition
Major Histocompatibility Complex
- MHC controls the expression of HLA.
- (Human Leukocytes Antigens)
Human Leukocyte Antigens
- 1st identified on WBCs
- They are present on all nucleated cells.
- Play a role in humoral and cellular immunity
- Antigen processing and recognition
- Bring antigen to cell surface so it can be recognized by T cells.
- Coding genes located on chromosome #6.
- Class I - Loci: A, B, C
- Class II - Loci: DP, DQ, DR
- Class III - Codes for complement and cytokines
Class I Antigens
- Present on all nucleated cells
- Highest expression on lymphocytes
- Antigen recognition by CD8 cytotoxic T cells
- Endogenous Pathway "Intracellular Watchdogs"
Class II Antigens
- Present on Lymphocytes, Monocytes/Macrophages, Dendritic Cells, Endothelium
- Antigen recognition by CD4 Helper T cells
- Bind EXOGENOUS protein
- Chemical messengers that influence the activites of other cells.
- Local mediators: Autocrine, Paracrine, Endocrine
IFN - Cytokine that interferes w/ viral replication
Tumor Necrosis Factor
TNF - Cytokine involved in innate defense against gram negative bacteria.
IL - Cytokine that communicates between leukocytes.
Role of Cytokines
- Chemokines - "call leukocytes"
- Growth factors - Colony stimulating factors
- Proinflammatory - TNF-a, IL-1, IL-6
- Immunosuppressive - IL-10
- Series of proteins that mediate inflammation and host defense reactions
- Most exist as zymogens
Role of Complement
- vascular permeability
- cell lysis
Activation pathway of complement
Complement Classical Pathway
- Triggered by antibody coated cell
- IgM (most efficient)
- IgG (1,2,3)
- Few substances can bind complement directly
- Stages: recognition unit, activation unit, terminal/MAC
Alternative complement pathway
- Antibody independent
- Triggered by: bacteria, yeast, fungi, viruses, parasites, tumor cells.
Lectin Complement Pathway
- MBL: binds to sugars in bacteria, yeast, viruses, and parasites.