Key molecules of immune system Flashcards
Difference between adaptive and innate immunity
Innate:
-rapid response (minutes, hours)
* fixed recognition elements
* limited specificity
* no memory
-Causes inflammation which can cause complications in body such as through chronic inflammation
Adaptive
* slow response (days to weeks)
* variable recognition elements
* highly specific
* immunological memory
(improved next response)
What are receptors, where are they found?
Receptors are proteins which can be modified by post-translational modifications.
Cell surface receptors- embedded in plasma membrane (e.g B-cell receptors)
Intracellular receptors include nuclear and cytoplasmic receptors.
What is the function of receptors?
Bind specifically to molecules (aka ligands) such as hormones, peptides, antigens etc.
This binding leads to conformational changes in the receptor which has downstream effects.
What are 4 molecules of innate system?
PRR, Cytokines, Complement System, Major histocompatibility Complex (MHC) molecules
What are the downstream effects when conformational change occurs in receptors?
1- activation of signalling cascade- leads to alteration of gene expression
2) Changes in membrane potential- leads to muscle contration
3) Changes in cytoskeleton- endocytosis in phagocytosis
What are cytokines?
Low molecular weight proteins
secreted by cells of the immune and other systems in
response to changes.
Perform signalling between cells with cell
communication and recruitment. Different types are produced by different cells and trigger different responses.
Include those produced early in the innate immune response activate further
defence mechanisms as well as local inflammatory responses.
Can be
◦ Autocrine – produced by and affects same cell
◦ Paracrine – produced and affects nearby cell
◦ Endocrine – produced by cell and circulates to cell it affects
Examples:
◦ tumour necrosis factor (TNF)
◦ Interleukin 1 (IL-1
Whats a complement and its function?
> 30 soluble and cell-bound proteins produced mainly by the liver but
also by cells of the immune system (e.g. monocytes, macrophages),
epithelial cells, etc.
Functions: recognition and destruction of extracellular pathogens by:
1) lysis of bacteria, cells and virus
2) Tagging pathogenic organisms and molecules and making them visible to immune cells for destruction (process called opsonization, which leads to phagocytosis)
3) Clearance of immune complexes from circulation
4) trigger inflammation and release of cytokines
What are antibodies and their function?
Soluble glycoprotein
molecules produced by the B lymphocytes (aka
B cells) of the adaptive immune system
Functions:
1-Neutralise pathogenic organisms, molecules and toxins
2- Tag pathogenic organisms and molecules and make them visible to
the immune cells for destruction (process called “opsonisation”)
* Activate the complement
* Activate particular immune cells to attack pathogens and damaged
host cells (“Antibody dependent cell-mediated cytotoxicity”, ADCC)
-Induce degranulation of particular immune cells, which can lead to
allergic reaction
What are 5 classes of antibodies, their structure and their function?
IgA- dimer or monomer - present on mucosal surfaces - protects against bacteria,viruses and toxins
IgD- momomer- function not yet fully known but considered to be in maintaining homeostasis
IgG- monomer- produced in secondary immune response- functions include neutralisation, opsonisation and complement fixation
IgE- monomer- plays a role in allergic reactions- protects against parasites
IgM- pentamer- produced in primary response- functions include opsonisation and complement fixation
Whats a MHC and its function?
Cluster of 200 genes found on chromosome 6. Determines tissue compatibility and rejection.
A group of proteins found on the surface of cells which present peptides from infecting microorganisms to
cells.
They fall into two different classes, class I or class II.
Class I MHC are found on all nucleated cells and bind to and present endogenous peptides.
Class II MHC are found on immune cells such as macrophages, dendritic cells and B cells. They bind and
present exogenous peptides to T cells.
What are PRR, which cells are they expressed on and what are examples of PRR?
Receptors on some immune cells that allow detection of a wide range of pathogens that share common
structures, known as pathogen associated molecular patterns (PAMPs).
PRR are found on macrophages, dendritic cells, monocytes
Examples of PRR include Toll-like receptos (TLR’s)
Examples of PAMPs include: lipids, proteins, nucleic acids such as lipololysaccharides and bacterial DNA.
Define the terms : Phagocytosis, Antigen Presentation and Apoptosis, Chemokines, Cytokines, Endocytosis
Phagocytosis
Phagocytosis is a process by which certain immune cells engulf and destroy microorganisms and
infected cells
Antigen presentation
Antigens from the engulfed material are then displayed to T cells to activate the adaptive immune
system on MHC II molecules.
Apoptosis
Apoptosis is programmed cell death-
Chemokines are cytokines which act as attractants (induce cell migration) and can be released by cells of the immune system as well as cells in the body. They include CL2, CCL3 and CCL5, CXCL1, CXCL2 and CXCL8
– e.g. CXCL8 attracts Neutrophils
Cytokines are molecules released by immune and non-immune cells which can have pro- or antiinflammatory effects. Examples include interleukins, interferons and Tumor necrosis factor (TNFa).
Endocytosis - a specialized form of transport by which very large molecules and insoluble materials are engulfed by invagination of the cell membrane forming intracellular vesicles
Explain the endogenous pathway of antigen procession and presentation (MHC)?
1- Intracellular proteins are tagged by ubiquitin.
2- Degraded by proteosomes into smaller peptide fragments (under normal conditions) or immunoproteasome (induced by TNF-a during immune response). (It enhances antigen processing during immune response)
3- Transported to ER via TAP and loaded onto MHC class 1 molecules.
4- Once the peptide is bound to MHC class 1, the complex is transported to the cell surface, where it can be recognised by CD8+ cells.
Why are viral proteins “endogenous” even though viruses come from outside?
Once a virus infects a cell, it hijacks the host machinery to produce viral proteins inside the cell.
Since these viral proteins are made inside the cell, they are considered endogenous and processed by the MHC class I pathway.
