Innate Immunity Flashcards
What is the complement system? What are the different pathways and how are they activated?
is a part of the immune system that
- enhances the ability of antibodies and phagocytic cells, promote inflammation, and attack the pathogen’s cell membrane
- all pathways converge onto a common terminal pathway (C3)
alternative pathway - spontaneously activated when complement binds to pathogen surface
classical pathway - activated by C1q binding to pathogen or triggered by antigen-antibody complex (opsonised microbe bound to antibody) binding to C1
lectin pathway - activated by mannose binding lectin (MBL - serum protein) binding to mannose proteins (MASP-1/MASP-2) on the pathogen surface
What is the function of
C3a
C3b
C5a
C5b, C6, C7, C8 and C9
C3a - anaphylatoxin
= acts as a chemoattractant and stimulates mast cell degradation causing histamine and 5-hydroxytrptamine (5-HT) release (vasoactive amines) which act on vasculature to vascular permeability and local blood flow (cause swelling, redness, heat and pain)
C3b - opsonin
= increases likelihood of phagocytosis as it attracts phagocytes by binding covalently to pathogens
C5a - anaphylatoxin
= acts as a chemoattractant, increases smooth muscle contraction, vasodilation and enhances vascular permeability
C5b, C6, C7, C8 and C9
= form membrane attack complex (MAC) and perforate the outer membrane of bacteria causing osmolysis
What is the function of dendritic cells?
are antigen presenting cells
- express MHC molecules (MHC I and II) that display microbial antigens and co-stimulators required for a full T cell response
antigen presentation normally occurs in the lymph nodes
- presents to T cells
- communicate with immature T helper cells in the lymph
How does opsonisation occur?
can occur via complement or antibody binding to the pathogen
- to increase likelihood of phagocytosis
IgG (most common type of antibody found in circulation) binds to the pathogen via Fab (antigen binding) region
- binding allows opsonised microbes to be captured by phagocytes
Fc regions of antibodies bind to the Fc receptors on the phagocyte
- all phagocytes have Fc receptors
Fc receptor signals activate phagocytes
- phagocytosis occurs
What is the function of cytokines?
to kill
to communicate
to amplify immune response
- can increase adhesion
- can increase migration
- can promote cell division
Which immune cell does NOT have MHC II that can bind to T helper cells? Which cells do have MHC II?
neutrophils do not have MHC II that T helper cells can bind to
- they die after phagocytosis via respiratory burst
the following cells DO have MHC II that T helper cells can bind to
- dendritic cells
- macrophages
- monocytes
What are the components of the adaptive immune system? What is their function?
cytotoxic T cells (molecular marker CD8)
- eradicate virus or infected and tumour transformed cells
helper T cells (molecular marker CD4)
- antibody production
- removal of bacteria and neutralisation of viruses
B cells (molecular marker CD20)
- differentiate into antibody producing plasma cells with the correct stimulus from helper T cells
What are MHC molecules? Where are they found? What is their function?
major histocompatibility complex
- are identifiable molecular markers that allow the body to identify between self and non-self
- displays antigenic contents of the cell on the cell surface to initiate immune cascade
MHC I - present products of protein synthesis
= all nucleated cells have them
MHC II - present products that entered the cell through digestion
= only phagocytic cells have them (macrophages, dendritic cells, B cells)
What is allorecognition? What are the different types?
occurs when T cells of an individual react to foreign MHC molecules of another individual
direct
- recipient T cells recognise intact allogenic MHC molecules expressed by a donor cell
indirect
- recipient T cells recognise a self MHC molecule that has bound a peptide derived from the foreign MHC molecule
linked/semi-direct
- uptake and surface expression of intact foreign MHC peptide complexes by recipient APC
What is the difference between MHC 1 and MHC 2?
MHC I - presents products of protein synthesis (made in the cell via the nucleus)
= e.g. infection
MHC II - presents products that enter the cell via digestion
What cells recognise antigens?
B cells
T cells
antibodies
- initiate the adaptive immune response
What is the function of T helper cells? How do they work?
T helper cells have T cell receptors complexed with a CD4 molecule
- recognise antigens that are complexed with MHC II
can differentiate into many subtypes
- 1, 2, 17 and T regulatory cell
stimulate B cells by binding to MHC on the B cell surface and releasing cytokines to activate them to produce antibodies
can activate macrophages and primed cytotoxic T cells via the release of cytokines
What is the function of cytotoxic T cells? How do they work?
cytotoxic T cells has T cell receptors (TCR) and are complexed with CD8 molecules
- recognise antigens that are complexed with MHC I
cytotoxic T cells needs to be primed
- after binding to an APC with an antigen/MHC I complex, it requires signals from other cells to be activated
= T helper cells release cytokines IL-6 and IFN to activate cytotoxic T cells
release cytotoxic granules into the pathogen
- granzymes and perforin
What is the function of B cells? How do they work?
B cells have B cell receptors that bind to antigens
- to be activated, the B cell internalises and presents the antigen on its surface in a peptide/MHC complex then travels to the cell surface
- it is activated by T helper cells releasing cytokines which cause activation
activation causes B cells to divide and differentiate into antibody producing plasma cells and memory cells
What are antibodies? What are the different types?
are globular glycoproteins that recognise and bind to pathogens with high specificity
- IgM, IgA, IgD, IgG (most common), and IgE
have an Fc region that binds leukocytes and Fab that binds pathogens
