IMMUNOSERO //STEVENS CHAP 2: NATURE OF ANTIGENS AND THE MAJOR HISTOCOMPATIBILITY COMPLEX Flashcards
responds to certain patterns
Innate immune system
characterized by recognition of individual pathogens
Adaptive immune system
key cells responsible for the specificity, diversity and memory in adaptive immunity
Lymphocytes
The immune response of lymphocytes is triggered by materials called
immunogens
Macromolecules capable of triggering an adaptive immune response by inducing formation of antibodies
or sensitized T cells in an immunocompetent host.
Immunogens
can then specifically react with such antibodies or sensitized T cells.
Immunogens
Refers to a substance that reacts with an antibody or sensitized T cells BUT MAY NOT be able to evoke an
immune response in the first place.
Antigen
FACTORS INFLUENCING THE IMMUNE RESPONSE
age, overall health, dose, route of inoculation, and genetic capacity
a system of genes that code for cell-surface molecules that play an important role in Ag recognition.
MHC
The ability of an immunogen to stimulate a host response
Immunogenicity
Characteristics of immunogenicity
Macromolecular size
Foreignness
Chemical composition and molecular complexity
Ability to be processed and presented with MHC molecules
the most effective immunogens bc made up of amino acids
Proteins & polysaccharides
Less immunogenic that protein bc smaller & have limited no. of sugars available to create structure
Carbohydrates
Examples of glycolipids
A, B, and H blood group antigens
Examples of glycoproteins
Rh and Lewis antigens
Key portion of the immunogen; the determinant site
Epitope
Molecular shapes of configurations that are recognized by B or T cells.
Epitope
sequential; aa following one another on a single chain
Linear epitopes
results from the folding of one chain or multiple chains
Conformational epitope
Anything that is capable of cross-linking surface Ig molecules: is able to
trigger B-cell activation
Nonimmunogenic materials that, when combined with a carrier, create new antigenic determinants.
Haptens
capable of reaction with antibody even when the hapten is not complexed to a carrier molecule
Haptens
Contains catechols which are haptens; once in contact with skin, these can couple with tissue proteins to
form the immunogens that give rise to contact dermatitis.
Poison ivy (Rhus radicans)
Best known for his discovery of the ABO blood groups; conducted most famous study of haptens
Karl Landsteiner
A substance mixed with an immunogen that increases the immune response in order to provide immunity to a particular disease.
ADJUVANTS
Work by: keeping the antigen in the area and by increasing the no. of cells involved in immune response
ADJUVANTS
Used to accelerate the immune response & increased the duration of protection, reduced need for booster
ADJUVANTS
actually work by targeting APCs , which are key to the adaptive immune response
Adjuvants
Antigens that belong to the host; do NOT evoke an immune response under normal circumstances
Autoantigens
Antigens from other members of the host’s species; Capable of eliciting an immune response
Alloantigens
Important to consider in tissue transplantation and in blood transfuions
Alloantigens
Antigens from other species, such as other animals, plants or microorganism.
Heteroantigens
that exist in unrelated plants or animals but are either identical or closely related in structure so that antibody to one will cross-react with antigen of the other
Heterophile antigens
Evidence now indicates that the genetic capability to mount an immune response is linked to a group of
molecules originally referred to as
Human Leukocyte Antigens (HLA)
gave name HLA bc 1st identified by discovering an antibody response to WBCs
Dausset
they determine whether transplanted tissue is histocompatible and thus accepted or rejected
MHC molecules
Encodes class l and II molecules which play a major role in antigen presentation to T cells
MAJOR HISTOCOMPATIBILITY COMPLEX
Actually found ON ALL nucleated cells in the body
MHC molecules
Play a vital role in the development of both humoral and cellular immunity
MHC molecules
Can function as antigens when transplanted from one individual to another
MHC molecules
Main function: To bring antigen in the body to the surface of cells for recognition by T cells
MHC molecules
Only occur when antigen is combined with MHC molecules on the surface of other cells
T-cell activation
The most polymorphic system found in humans; so many different alleles
MHC system
Genes coding for the MHC molecules in humans are found on the
short arm of chromosome 6
Found at 3 different locations or loci termed A, B, and C
Class I genes
there is only one gene coding for each particular molecule
class 1 molecules
Involved in antigen recognition ; they influence the repertoire of antigens to which T cells can respond
Class I and II genes
Can be seen in most nucleated cells
Class I genes
Can be seen in most antigen-presenting cells
Class II genes
situated in the D region and there are several diff. loci known as DR, DQ and DP
Class II genes
Have one gene that codes for the alpha chain and one or more genes that code for the beta chain
Class II genes
Code for the C4A, C4B, C2 and B complement proteins, & cytokines such as tumor necrosis factor (TNF)
Class III genes
these are secreted proteins that have an immune function, but they are NOT expressed on cell surfaces
Class III genes
Also have a completely different
structure compared with the other two classes
Class III genes
Expressed on all nucleated cells
Class I MHC (HLA) molecules
Found primarily on APCs
Class II MHC (HLA) molecules
CLASS I MHC MOLECULES are Highest on
Lymphocyytes and Myeloid cells
CLASS I MHC MOLECULES are Low/Undetected on
Hepatocytes, neural, muscle cells & sperm
expressed at a much lower level than HLA-A
HLA-C antigens
the most important to match for transplantation
HLA-A and HLA-B antigens
Nonclassical Class I antigens
G,E, F
on fetal trophoblast cells; bind to NK inhibitory receptors and turn off the NK cytotoxic response (protect fetus)
G antigens
Class II MHC molecules: found on the APCs that include:
B lymphocytes
Monocytes
Thymic epithelium
Macrophages
Dendritic cell’s
highest levels of class II molecules on their surfac
Dendritic cells
The major class II molecules: DR, DP, DQ; consist of two noncovalently bound polypeptide chains that are encoded by separate genes in the MHC complex; called _______
heterodimers
expressed at the highest level bc it accounts for about one-half of all the class II molecules
DR
found in the shortest supply
DP
Nonclassical Class II antigens
DM, DN, DO
helps to load peptides onto class II molecules
DM
Nonclassical Class II antigen that modulates antigen binding
DO
process by which degraded peptides w/in cells are transported to plasma membrane where T cells can then recognize them.
Antigen Presentation
Watchdogs of viral, tumor, and certain parasitic antigens that are synthesized within the cell
Class I molecules
Help to mount an immune response to bacterial infections or other pathogens found outside cells
Class II molecules
Known as the ENDOgenous pathway of antigen presentation bc antigens that bind to class I proteins are actually synthesized in the same cell as the class I molecules
CLASS I MHC – PEPTIDE INTERACTION
Participate in EXOgenous pathway of antigen presentation. This means that antigen is taken into the cell from the outside by means of either phagocytosis or endocytosis
CLASS II MHC – PEPTIDE INTERACTION
8 to 16 amino acids
CLASS I MHC
Class II molecules are synthesized in the ER and associate with a protein called
invariant chain (Ii)
