Introduction to Immune System Flashcards
What is the innate immune system?
your ever-present defence against infection. It is made up of barriers that keep viruses, bacteria, parasites, and other foreign particles out of your body or limit their ability to spread and move throughout the body.
What does the innate system include?
- Epithelial barriers to the environment (eg skin, gastro-intestinal tract, respiratory tract) that prevent microbe entry.
- Secretions at mucosal surfaces – flushing action and antimicrobial properties.
- Cells that are resident in tissues (eg mast cells) or circulating in the body (eg neutrophils).
- Circulating proteins in the blood (eg complement proteins).
- Cytokines (eg interferons) that are locally produced by infected cells.
What are the main functions if the innate immunity?
- Prevention, control and elimination of infection
- Removal of damaged cells and initiation of tissue repair
- Activate the adaptive immune response
What are some important features of the innate immunity?
- Response to microbes and products of injured cells
- Non-specific activity
- No “memory”, the response is the same to repeated challenge
How do immune cells know when to get to work?
detects “danger” through a series of pathogen-associated molecular patterns (PAMPs) or damage-associated molecular pattern molecules (DAMPs).
What are PAMPS?
small molecular motifs conserved within a class of microbes
Give examples of PAMPS
glycans, lipopolysaccharides, bacterial flagellin, lipoteichoic acid, peptidoglycan and nucleic acid variants normally associated with viruses such as double-stranded RNA.
What are DAMPs?
molecules released by stressed cells undergoing necrosis
Give examples of DMAPs
heat-shock proteins and cytokines.
Non-protein DAMPs include ATP, heparin sulfate, and DNA.
What molecules recognise PAMPs and DAMPs?
Pattern Recognition Receptors (PRRs) on immune cells
What type of cells carry out phagocytosis?(3)
neutrophils, macrophages and dendritic cells
Phagocytosis is part of what immune response?
adaptive immune response
Define inflammation
is the process whereby immune cells (which are normally distributed throughout the body) can be recruited and concentrated to a site of infection or damage.
What happens after PRRs recognise DAMPs and PAMPs?
trigger proinflammatory and antimicrobial responses by inducing the release of a broad range of cytokines from white blood cells.
What are the three main events of inflammation?
- Increased blood supply to the affected area;
- Increased permeability of the vasculature ;
- Migration of WBCs out of the blood capillaries into the affected tissue.
Describe the adaptive immune system (4)
- Potent;
- Responsive to any potential foreign entity;
- Highly specific; and
- Has memory.
What are the main components of the adaptive immune systems?
- Dendritic cells
- T lymphocytes
- Cytokines
- B lymphocytes
What is the purpose of dendritic cells?
capture, process and present antigens.
Describe dendritic cells(4)
• Widely distributed in lymphoid tissues, mucosal epithelium and body organs
- Important in phagocytosis
- A vital link between the innate and the adaptive immune systems
• Antigen processing and antigen presentation to T lymphocytes
What are T-lymphocytes?
control the immune response by providing “help” to B cells and macrophages (helper T cells); direct killing of infected or tumour cells (cytotoxic T cells).
What are cytokines?
soluble proteins secreted mainly by T cells that control activities of other cells.
What are B-lymphocytes?
produce and secrete antibodies, proteins that specifically bind target molecules (antigens) on microbes or cells.
What is the lymphoid system?(2)
- Immunological cells are largely organised into tissues and organs for best efficiency.
- Collectively, these structures are known as the lymphoid system.
What are primary lymphoid organs?
the sites of maturation of white blood cells – they differentiate from stem cells, multiply, are programmed and mature into functional cells.
What are secondary lymphoid organs?(2)
organs provide the site for interaction between antigens and WBCs. They also allow spread of the immune response.
• Secondary lymphoid organs are associated with systemic and mucosal immune compartments
What is the lymphatic system?
part of the circulatory system
It comprises a network of lymphatic vessels that carry lymph fluid and cells from the tissues back into the blood stream.
What are lymph nodes?
organised structures at regular intervals along the lymph vessels
What is the advantage of the dense concentration of immune cells?
provides an ideal environment for initiating immune responses and communication between immune cells
Describe the journey of lymph after it arrives at a node(3)
Lymph arrives at the node by an afferent lymphatic vessel,
- it filters through multiple layers of antigen presenting cells,
- T cells and B cells, and exits via the efferent lymphatic vessel.
What is the hallmark of adaptive immunity?
the ability to specifically recognise foreign antigens
What are the two types of molecules involved in recognition of foreign antigens?
- Immunoglobulins (Igs)
2. T-cell antigen receptors (TCRs)
What are immunoglobins?
glycoproteins produced by plasma cells. They specifically recognise and bind strongly to particular antigens on pathogens, and prevent disease or aid in the destruction of the pathogen.
Igs are produced by what type of cells?
plasma cells, B-cells in humoral immunity
What is the role of T-cell antigen receptors?
They are responsible for recognizing processed fragments of antigen (peptides) which are “presented” by host cells
Describe the binding between TCR and antigen peptides
relatively weak compared to antibodies.
What happens when TCR engages with antigenic peptide?
the T lymphocyte is activated through a series of biochemical events (signal transduction), leading to cell proliferation and biological activity (eg cytokine production).
TCRs are produced by…
T cells – cellular immunity
What are B-cells?
lymphocytes, which when activated, become plasma cells and then produce antibodies
What do antibodies do?
- targets, or recruit other components of the immune system to kill targets.
- They bind specifically and with high affinity to “non-self” antigens.
- can neutralise targets, or recruit other components of the immune system to kill targets by Fc mediated effector functions.
What is our body’s repertoire for antibodies?
10^15
What type of cells can T-cells recognise?(2)
only recognise antigens that have been processed within cells, and that are displayed on cell surfaces.
- eg antigens derived from pathogens that that have infected cells, such as viruses or intracellular bacteria, or from pathogens that have been phagocytosed by antigen presenting cells like macrophages and dendritic cells
What molecules on the surface of cells display antigen peptides?
the major histocompatibility complex (MHC).
What do mature T-cell cytotoxic cells do?
kills target cells using cytokines, cytotoxic granules, and the caspase cascade
What do mature helper T-cells do?
secrete cytokines to help activate macrophages, B-cells and other T cells
How do T-cells recognise antigens
via cell-surface receptors (TCRs) proteins, that are related to antibodies
Describe one difference between antibodies and T-cells in recognising foreign molecules
unlike antibodies, T cells do not recognise foreign molecules in their “native” state.
What are the two valuable features of antibodies in laboratory assays?
antigen specificity and high affinity binding
Name 4 Immunological techniques in diagnostics and research
- ELISA
- Western blotting
3 .Lateral flow assay - Fluorescence- activated cells sorting
compare the innate and adaptive immune system
→in the innate system, we have macrophages, neutrophils, dendritic cells
→ in the adaptive system, we have lymphocytes
→ the innate system acts faster than the adaptive system
→ the innate system does not hold any ‘memory’, while the adaptive system does
→the innate system is not specific, while the adaptive system is very specific
→ the innate system has a small number of microbial ligands that are highly conserved between pathogens
→ the adaptive system has billions of possible antigens
→the innate system has germ-line encoded receptors evolved by natural selection which don’t change
→the adaptive system has receptors that are generated randomly within the individual, they can’t be inherited
there are specific diseases associated with innate immunity what are they?
→complement
→ core defects (eg. C3) linked to the development of autoimmune diseases such as lupus
complement
→ non-core defects linked to susceptibility to specific types of pathogens such as Neisseria (meningitis)
macrophage deficiencies
→ chronic granulomatous disease (CGD); no oxidative burst for bacterial killing
macrophage deficiencies
→ IRF8 (transcription factor) mutations linked to susceptibility to TB
→ Aicardi-Goutieres syndrome is associated with constitutive production of inflammatory cytokines (defect in regulation of cytokines)
→ lack of interferon-responsiveness
→ sensitivity to viral infections (eg. measles)
how are natural killer cells activated?
Natural killer (NK) cells are activated by loss-of-self.
→An NK cell has an MHC receptor on its surface.
→With an uninfected cell, it will present the ligand for the MHC receptor, stimulating an inhibitory signal that stops the NK cell from killing it.
→ with an infected cell, they do not present this ligand, so the inhibitory signal is not presented
→releases perforin and cytotoxic granules into the infected cell or engages the cell’s death receptors.
how does interferon work?
→A virus infects a cell, which then becomes known as the primary infected cell.
→ virus will multiply inside the cell, and, after the cell dies, it will release the viral progeny.
→as the primary infected cell is dying, it releases interferons.
→interferons are picked up by other healthy cells, and they induce the transcription of >400 antiviral genes.
→ healthy cells in an antiviral state so viruses cannot affect them.
what are the three types of PRR?
EXTRACELLULAR:
→they recognize PAMPs outside of a cell and trigger a coordinated response to the pathogen
INTRACELLULAR (CYTOPLASMIC):
→recognize PAMPs inside a cell and act to coordinate a response to the pathogen
SECRETED:
→act to tag circulation pathogens for elimination
