Cells of the immune system Flashcards
What are the soluble factors of the innate immune system?
- antibacterial
- complement system
What are the cellular factors of the innate immune system?
- scavenger phagocytes
Name two examples of antibacterial factors
- lysozymes
- lactoferrin
What is lysozyme and what does it do?
- enzyme present at mucosal surfaces
- active in breaking down the gram positive cell wall
What is lactoferrin and what does it do?
- protein found at mucosal surfaces
- chelates iron and reduces amount available in GI/respiratory tract, therefore inhibiting the growth of bacteria
What is complement
soluble factor of the immune system that can be present on mucosal surfaces but is very active in blood
What is the complement cascade?
enzymatic cascade with three ways of activation, culminating in a common activation pathway and resulting in different effects
Describe the classical pathway
Part of the complement cascade
The antibody-antigen complex creates a conformational change in the Fc region, allowing complement binding and activation
Describe the alternative pathway
Part of the complement cascade
Complement activated directly on pathogen surface
What are the key responses of the complement system?
- capable of killing bacteria by itself
- can opsonise pathogens to flag them for removal
- recruits inflammatory cells to the area
How does complement lead to the destruction of pathogens?
In the late steps of complement cascade, complement proteins form membrane attack complex, allowing them to ‘punch’ holes in the bacterial membrane causing lysis.
What are the scavenger phagocytes?
- macrophages (present in tissues normally)
2. neutrophils (enter tissue when inflammation present)
What bacteria can survive within macrophages for years?
mycobacterium tuberculosis
What are macrophages?
White blood cell derived from blood monocytes
What are the functions of macrophages
- phagocytosis
- antigen presentation
- cytokine production
Describe the role of macrophages as an APC
processes engulfed particles, travels to draining lymph nodes and presents to T cells in MHC class II
What cytokines do macrophages produce?
Inflammatory = TNF alpha Regulatory = IL10
What are pattern recognition receptors?
E.g. Toll-like receptors
recognise molecules found commonly in micro-organisms
able to recognise extracellular and intracellular threats
What are neutrophils
First cell to respond to infection through the innate immune system due to chemotaxis
What are the roles of neutrophils?
- phagocytic
- degranulate
- die locally
How do neutrophils migrate towards areas of infection
Neutrophils migrate towards bacterial products (e.g. LPS), chemokines and ‘danger signals’ (e.g. complement components)
How do neutrophils phagocytose pathogens?
using proteases, reactive oxygen species, lysozymes, etc.
What is the purpose of neutrophil degranulation?
Releases toxic granules extracellularly.
- helps destroy pathogens
- releases long strands of DNA to help tangle and trap the pathogens to further expose them to chemicals
What is the result of neutrophils dieing at the site of infection?
produces characteristic pus
What is the main role of eosinophils
respond to parasites and have a role in allergy
What substances are released from eosinophils on degranulation?
- major basic protein
- eosinophil cationic protein
- eosinophil peroxidase
released onto surface of parasite
What is the main role of basophils?
Mast cells
- found at mucosal sites as a ‘guard’
- important role in allergy
Describe degranulation of mast cells
reapid release of pre-formed granules containing cytokines and mediators, e.g. histamine
What cell links the innate and adaptive immune systems?
dendritic cell
What is the role of the dendritic cell?
sits in tissue and projections sample the environment for signals to activate the immune response
What are the processes dendritic cells are involved in?
- phagocytosis
- migration
- antigen presenting
Describe the role of dendritic cells in antigen presenting
Present to CD4 T cells and can initiate an adaptive immune response
What are the main subdivisions of the adaptive immune response
- humoral
- cellular
What mediates the humoral immune response?
- B cells
What mediates the cellular immune response?
- CD4 T cells
- CD8 T cells
What is the role of CD4 T cells?
facilitate the immune response without partcipating in killing
What is the role of CD8 T cells?
cytotoxic T cells, which are directly involved in killing cells
What are the main functions of antibodies?
- opsonisation for phagocytosis
- activation of complement for lysis
- neutralising toxins and pathogen binding sites
What are the main antibody isotypes?
- IgM
- IgG
- IgA
- IgE
What are the features of IgM
main antibody of primary immune response
- low affinity
- activates complement
What are the features of IgG?
Main antibody of the secondary immune response
- Higher affinity
- Activates complement
- binds Fc receptor on phagocytes
- crosses placenta
What are the features of IgA?
present in secretions and lines epithelial surfaces
neutralises by blocking binding of pathogens
What are the features of IgE?
high affinity binding to mast cells through Fc receptor
- role in allergy
What stimulates B cell activation?
Presentation of an antigen via APC and the addition of helper T cell or other stimuli
What step occurs once a B cell is activated?
Clonal expansion
What are the ways in which a B cell can differentiate?
- Develop into plasma cells
- undergo istype switching
- generate memory B cells
What is the T cell receptor?
Multi-protein receptor on surface of T cells that only recognises an antigen if it is bound to an MHC molecule
- only recognises short peptide lengths
What is the ‘second signal’
Activation of lymphocytes requires both the present of ann antigen and the presence of a danger signal’.
Without second signal, the cell will become anergic
Describe MHC class 1
- presents to CD 8 T cells
- found on all nucleated cells
- Presents intracellular antigen (allows recognition of viral infected or cancer cells)
Describe MHC class 2
- presents to CD4 T cells
- presents extra-cellular derived antigen (phagocytosed)
- found on antigen presenting cells (DC’s, macrophages, B cells)
What are the main groups of specialist CD4 cells?
- Th1
- Th2
- Th17
What is the role of Th1?
predominantly secretes interferon gamma and are though to be involved in intracellular immunity
What is the role of Th2?
predominantly produces IL4 and are though to be responsible for antibody mediated responses
What is the role of Th17?
produces IL17, which are important at the mucosal surface
What are the main areas of note in the lymph node?
- primary follicle
- paracortical area
- medullary cords
What process occurs in the primary follicle?
inactive B cell sampling
What process occurs in the paracortical area?
T cell sampling
What process occurs in the medullary cords?
Macrophages and plasma cells are leaving the lymph node
