NATURE OF ANTIGENS AND MAJOR HISTOCOMPATIBILITY COMPLEX Flashcards
It is a substance that is specifically recognized by the adaptive immune system
ANTIGEN
All antigens are immunogens, but not all immunogens are antigens
T or F
F
All immunogens are antigens, but not all ANTIGENS are Immunogen
Factors influencing the Immune Response
Age
Dose
Route of Inoculation
Health status of the host
Genetics
It is the ability of an immunogen to stimulate a host response
IMMUNOGENICITY
What are the traits of immunogen
Macromolecular size
Chemical composition and molecular complexity
Foreignness
Ability to be processed and presented with MHC molecules
It is a precise molecular shapes or configuration recognized by B cells, it binds to an antibody or T cell receptor
EPITOPE
A low molecular weight molecule that is too small to stimulate an immune response but when combined with other molecule can induce response
HAPTENS
2 types of Epitopes
Linear Epitopes- consist of sequential amino acids on a single polypeptide chain
Conformational Epitopes- result from the folding of one or more polypeptide chains
It is a substance administered with an immunogen that increases/enhance the immune response
ADJUVANTS
Antigens that belongs to the host
AUTOANTIGEN
Antigen that are from other members of the host species that is capable of eliciting an immune response
ALLOANTIGEN
Antigen that is from other species such as other animals, plants or microorganisms
HETEROANTIGENS
Antigens that exist in unrelated plants or animals but are identical or closely related in structure
HETEROPHILE ANTIGENS
A large multi-gene locus consisting of several thousand kilobase pair of DNA on a single chromosome
MAJOR HISTOCOMPATABILITY COMPLEX
HLA is located in which chromosome?
Chromosome 6
A class of MHC in which molecules are coded for at 3 different locations or loci termed A, B, C
Class I molecules
Class of MHC that is situated in the D region and there are several different loci known as DR, DQ, DP
Class II genes
Class of MHC which code for complement proteins and cytokines such as tumor necrosis factor
Class III genes
CLASS I MHC MOLECULES
Cellular Distribution: All Nucleated Cell
Structure: Alpha Chain & Beta2-microglobulin
Classes: A,B,C
Size of Peptides Bound: 8 to 11 amino acids
Nature of Peptide binding cleft: CLOSED at both ends
Interaction with T-cells: present ENDOGENOUS Antigen to CD8 =T-cytotoxic cells
CLASS II MOLECULES
Cellular Distribution: B cells, Thymocytes, Macrophages, Dendritic cells, Thymic epithelial cells
Structure: Alpha Chain & Beta chain
Classes: DP, DR, DG
Size of Peptides Bound: 13 to 18 amino acids
Nature of Peptide binding cleft: OPEN at both ends
Interaction with T-cells: present EXOGENOUS Antigen to CD4 =T-helper cells
A phenomenon in which T cells recognizes transported cells bind with peptides in the plasma membrane
ANTIGEN PRESENTATION
Class I MHC-Peptide Presentation Pathway
- Endogenous antigen within the cytosol is degraded by proteasome
- Peptides are transported to the ER by TAP (transportes associated with Ag processing)
- Alpha chain binds to Beta2-microglobulin
- Alpha chain binds to peptide
- Peptide-Class I is transported to Golgi complex and unto the cell surface
- Class I MHC binds to CD8+T cell
- If CD8 recognizes the antigen, cytokines will be released causing destruction of target cell
Class II MHC-Peptide Presentation Pathway
- Class II MHC binds invariant chain to block binding of endogenous antigen
- MHC complex goes through Golgi Complex
- Invariant chain is degraded leaving CLIP fragment
- Exogenous antigen taken in and degraded and routed to intracellular vesicle
- CLIP fragment exchanged for antigenic peptide
- Class II MHC antigenic peptide is transported to the cell surface
- Class II MHC peptide complex binds to CD4+ T cell
- Upon recognition, clonal expansion will take place and will secrete cytokines that cause antigen-activated B cell to proliferate and produce plasma cells that will create antibody.
