Immunology 1- Introduction to the immune system Flashcards
What does the immune system need to do to function
Detect there is a “threat”
Respond effectively against the “threat”
Minimise “collateral damage”, return to healthy self
If necessary, remember the “threat” to respond more
effectively if it is met again
What is meant by immunology
The study of physiological mechanisms that we use to defend our bodies against invasion from other organisms, primarily microorganisms. The immune system is crucial to human survival, in patients with immunodeficiencies, even minor infections can be fatal, can also increase susceptibility to cancer.
Why is knowledge of the immune system important
Allows its manipulation to improve human health i.e vaccines, immunotherapy, diagnosis (levels of antibodies).
What is the immune system
Complex cellular and protein network that has evolved to protect the host from pathogenic microbes
What are the consequences of an abnormal immune response
Abnormal function or regulation of the immune system may lead to disease, e.g. autoimmune diseases, allergy
Why is it important that the immune system has a healing role too
The immune system has powerful defence mechanisms, which can destroy our own cells, hence need to play a healing role too. Hence the immune system is Also involved in homeostasis e.g. tissue repair
How does the immune system identify and eliminate harmful microorganisms and harmful substances such as toxins.
by distinguishing ‘self’ from ‘non-self’ (sometimes ‘normal self’ from ‘abnormal self’ in cancer)
and
by identifying ‘danger’ signals, including tissue damage
Can the immune system have receptors for neurotransmitters
Yes
How can the immune system be described as a sensory system
Stress and food can effect the immune system, but the immune system is not a separate entity,
but is fully integrated into other body systems, hence it is described as a sensory system that can move.
What is meant by immunopathology
Damage to cells caused by the mechanisms of the immune system- often collateral damage in the immune response to a foreign antigen.
What is the importance of the danger signal in an immune response
Only immune responses initiated against appropriate non-self antigens, this means it will not respond to the antigens expressed on the surface of food molecules for example.
Can the immune system respond to tissue damage in the absence of infection
Yes
Describe the evolutionary arms race between humans and bacteria,
The host exerts selection on the pathogen; the pathogen exerts selection on the host Only humans with effective immune systems will survive, only bacteria that can invade human tissue effectively will survive.
What are the consequences of the evolutionary arms race between humans and pathogens
The pathogen replicates millions of times faster than the host - and so can evolve faster
The host therefore relies on a flexible and rapid immune response
Our most polymorphic (variable) genes are those that control the immune response: this variation has been
selected for by exposure of populations to infectious diseases
What are the two strategies used by immune system cells to recognise foreign antigens
Strategy 1
Recognise molecular patterns- could be carbohydrates found on pathogens
Hundreds of receptors
Germ-line encoded
Strategy 2
Recognise precise structure
Millions of receptors
Generated by random recombination of gene segments
Why do we need to utilise recombination of gene segments to produce different receptors that recognise different antigens
Limited number of germ-line encoded receptors in each individual to recognise all the foreign antigens, would be impossible to have millions of genes coding for each specific receptor.
What are the advantages of germ-line codes receptors
Many cells can express the same
receptor, allowing a rapid, effective
response.
Limited receptor diversity, some pathogens
may not be efficiently recognised.
What are the advantages and disadvantages of having receptors encoded by the random recombination of gene segments
Initially very few cells express a specific
receptor, so they must be greatly expanded
to generate an effective response. This
takes time.
Massive diversity of receptors, all structures may potentially be recognised. However, because of random nature of receptor generation, there is potential for autoimmunity.
Why is it important that lymphocytes are tightly regulated
Due to the nature of the recombination process, the receptors generated have the potential to recognise self-tissue, hence the production of lymphocytes must be tightly regulated to avoid autoimmunity.
What are the two types of ‘triggers’ recognised by Pattern Recognition Receptors
PAMPs – Pathogen-Associated Molecular Patterns
DAMPs – Damage-Associated Molecular Patterns- from normal self-patterns- release of their contents- ATP, DNA, heat shock proteins such as uric acid and fragments of the ECM ( especially galectins)- act as receptors for PRRs.
Give examples of PAMPs on bacteria
Flagellin, LPS, Proteoglycan
Give examples of PAMPs found on viruses
Envelope glycoproteins, unmethylated CpG motifs, ssRNA, dsRNA
Give examples of PAMPs found on fungi
Mannoproteins (cell wall), Phosphlipomannans, Beta Glucans (sugar found in cell wall), Unmethylated CpG motifs
Give examples of PAMPs found on parasites
profilin- actin-binding molecule, glycolipids, DNA.
Describe the difference between T cell and B cell antigen receptors
The B cell antigen receptor is a membrane-bound antibody
- binds intact antigens - found in the humour
Expressed on the T cell surface are 2 protein chains (α and β) which together make the
T cell receptor (TCR)
- binds ‘processed’ antigen fragments presented at cell surfaces
Which part of the antigen does the antigen receptor bind to
the epitope
What does each clone of B cell and T cell carry
Each clone of B cells or T cells has a unique receptor, specific to one antigen; each cell carries many copies of this receptor on the cell surface.
Describe the characteristics of innate immunity
independent of previous exposure
broad specificity
depends on pre-formed and rapidly synthesised components
fast (starts in minutes/hours)
limited specificity –
pattern recognition
of ‘danger signals’
Describe the characteristics of adaptive immunity
an adaptation to exposure (also called acquired immunity)
depends on clonal
selection: i.e. expansion of cells
or antibodies, selected for
antigen specificity
slow (starts in days)
highly specific to foreign
antigens
What is the basic role of interferons
To interfere with pathogen functions.
What is the purpose of the innate immune response
destroys invading nucleic acids (e.g. viruses) in the cytoplasm
activates inflammatory pathways, signals for recruitment of immune system cells to sites of damage/infection
elicits type 1 interferons, for anti-viral defence
two main consequences:
“buys time” while the adaptive immune response starts
promotes and directs the appropriate adaptive immune response
What are the effector arms used by the adaptive immune system
Cellular immunity
T and B lymphocytes
Humoral immunity
antibodies
What are the cells of the adaptive immune system
Lymphocytes (agranular leukocytes)
20-40% of the circulating WBCs, 99% of the cells in lymph
- T (Thymus-derived) cells - B (Bone marrow-derived) cells Each subset has distinct cell-surface molecules e.g. CD4 on helper T-cell Basophils, mast cells, dendritic cells, Natural Killer Cells
What are the cells of the innate response
Neutrophils, eosinophils, macrophages, basophils, mast cells, dendritic cells, Natural Killer cells
What are the soluble factors used by the adaptive response
Cytokines and antibodies
What are the soluble factors utilised by the innate response
Acute phase proteins
Complement
Cytokines
Describe the generation of clonal diversity in B and T lymphocytes
During B and T cell development, random genetic recombinations occur within each cell among multiple copies of immunoglobulin gene segments (B cells) or TCR gene segments (T cells). =strategy 2.
These processes generate the diversity of clones of lymphocytes: each clone is specific to a different antigen.
Describe the consequences of the clonal diversity in the adaptive immune response
Each lymphocyte carries a single, unique antigen receptor.
There are millions of lymphocytes in the body, and thus millions of different antigen receptors.
Lymphocytes that meet an antigen they recognize will proliferate and survive.
The huge majority of lymphocyte clones will die out.
Describe the process of clonal selection
A typical antigen is recognized by 1 in ~105 naive T cells.
98% of T cells are in the lymph circulation and organs; 2% in blood
Antigen binds to surface receptor on the B cell or the T cell and causes selective expansion of that clone = clonal selection
Effector lymphocytes are produced which bind to complementary antigens to eliminate the infection.
What happens when the antigen is removed from the body
Most lymphocytes that have proliferated recently will die after fulfilling their function
Some survive as memory cells: this forms the basis of vaccination
Re-exposure to a previously encountered antigen leads to a more rapid and greater immune response (secondary response)
What are antigens
molecules that react with and are bound by antibodies or T cells. However, not all antigens can induce an immune response in the host, those that can are termed immunogens.
What are antibodies
immunoglobulins found in the blood and body fluids, produced in response to foreign antigen and bind specifically to the foreign antigen. They are an adaptive component of the humoral (soluble, non-cellular) immune response.
What are lymphocytes
Mononuclear cells that are part of the leukocyte lineage, named as they are the main cell type found in the lymph. All cells of the immune system are derived from stem cells in the bone marrow.
What is meant by naïve lymphocytes
lymphocytes that have never encountered the antigen complementary to their cell surface receptor, and thus have never responded to it.
What is the purpose of memory lymphocytes
Product of an immune response, ensuring that the specificity of their antigen receptor remains in the pool of lymphocytes in the body.
What is active immunity
The induction of an immune response within an individual by the introduction of an antigen.
What is passive immunity
immunity gained without antigen induction of a response i.e by a transfer of antibody, immune serum, or activated lymphocytes into a naïve recipient.
What is meant by the primary response
response made by naïve lymphocytes when they first encounter their specific antigen.
What is meant by the secondary response
response made by memory lymphocytes, when they re-encounter their specific antigen.
What happens to the lymphocytes that do not encounter their specific antigen
They die. the overall size of the total peripheral lymphoid pool is regulated by homeostatic mechanisms.
Which lymphoid tissue are antigens which present in the blood taken to
The spleen.
Describe the importance of the organisation of the immune system
The physiological organisation of the immune system is important to its function. The physical organisation is essential to allow adaptive responses against danger anywhere within the body. The lymphatic system drains fluid from tissue cells via lymph nodes, through which lymphocytes recirculate. The tissues are patrolled by lymphocytes, antibodies and antigen-presenting cells.
Which responses does gut-associated lymphoid tissue control
Responses in the intestinal tract.
What is the first line of defence
The innate immune system
What does clonally distributed mean
That unique receptors are found on each lymphocyte.
