Immunology Flashcards
What is the life span of a mature erythrocyte?
90 days
What system removes old and damged red blood cells?
Reticuloendothelial system
What is the function of the mature erythrocyte?
Contains haemoglobin to transport oxygen and carbon dioxide to and from cells
Where are mast cells found?
Connective tissues and mucous membranes
What do the granules of mast cells contain?
Histamine
What is the function of mast cells?
Important role in allergy
Main cell targets are parasites
Activated by cross-linking of IgE antibodies bound to their FC receptors
Activation results in mast cell degranulation
Where is basophil found?
Bone marrow and circulation
What is the function of basophils?
Main cell targets are parasites
Activated by cross-linking of IgE antibodies that they have bound to their FC receptors
Activation results in basophil cell degranulation
Also capable of phagocytosis
What is the function of neutrophils?
First cells to migrate to the site of the infection
Main cell targets are extracellular pathogens like bacteria and fungi
Phagocytosis
Degranulation
What is the life span of basophils?
Hours to days
What is the life span of neutrophils?
A few days
What is the function of eosinophil?
Targets multicellular parasites too big for phagocytosis
Important role in allergy
What is the life apn of eosinophils?
8-12 days
What is the function of a monocyte?
Migrates to tissues, where they become macrophages and dendritic cells in response to inflammation
Capable of phagocytosis
Possess large quantities of hydrolytic enzymes
What is the life span of a monocyte?
˜ 24 hours
When do the specialised cells of the immune system originate and develop in the bone marrow?
During haematopoiesis
What cell do the specialised cells of the immune system originate from?
A common progenitor cell => haematopoietic stem cell
What does the haematopoietic stem cell divide into?
Common myeloid progenitor
Common lymphoid progenitor
What does a monocyte divide into?
Macrophages and dendritic cells
What is the function of macrophages?
Phagocytosis
Professional antigen presenting cell - antigen presentation to CD4+ Th cells
Cytokine release: TNF-alpha, IL-2, IL-6
TNF-alpha
Tumour necrosis factor alpha
What is the life span of macrophages?
Months to years
What is the function of dendritic cells?
Professional antigen presenting cell
Phagocytosis
Antigen presentation to CD4+ T cells via MHC II
Cytokine secretion: TNF alpha, IL-12, IL-23
What is the function of natural killer cells
Activated by IFN and macrophage derived cytokines
Activated by abnormal MHC I signals - e.g. by cancerous cells or virally infected cells - to cause apoptosis of the cell
What does a small lymphocyte divide into?
T and B lymphocytes
Which type of immunity shows immunilogical memory?
Adaptive
Innate immunity shows no immunological memory
How do nucleated cells display self-markers to reassure the immune system and prevent unnecessary reactions?
Via a cell membrane protein called the Major Histocompatibility Complex I (or MHC I)
HLA
Human leukocyte antigen, or MHC
MHC
Major Histocompatibility Complex
What is haematopoesis and where does it occur?
The development of mature blood cells from pluripotent stem cells in the bone marrow and foetal liver
What are cytokines?
Proteins produced by many different cells that mediate inflammatory and immune reactions. Act as the principle mediators of communication between immune cells
Where are MHC I molecules found?
On the cell surface of all nucleated cells in the body
Where are class II MHC molecules found?
Only on professional antigen presenting cells
What is the function of class II MHC molecules?
Present exogenous, or extracellular antigens from pathogenic invaders
Examples of professional antigen presenting cells
Dendritic cells
Macrophages
B lymphocytes
What are professional antigen presenting cells responsible for?
Bringing antigens to the attention of T lymphocytes via class II MHC molecules
Why are antigen presenting cells necessary?
T lymphocytes are unable to recognise and react to free floating antigens
How can immunological tolerance be classified?
Central or peripheral - depending on where the state of tolerance is initiated
Where is central tolerance developed?
Within primary lymphoid organs
Where do T lymphocytes develop central tolerance?
Within the thymus
Where do B lymphocytes develop central tolerance?
Within the bone marrow
Where is peripheral tolerance created?
Within secondary lymphoid organs, containing mature immune cells that have already been released into the circulation
What are some physical or chemical barriers that help prevent the human body from pathogen invasion?
Lysozyme in tears, saliva and sweat
Mucociliary escalator
Intact skin surface with sebum to lower pH
Intact mucosal membranes
Acidic pH of stomach
Rapid pH change in duodenum and alkaline pH in jejunum and ileum
Normal flora in bowel and vagina and on skin surface
Flushing of urinary tract
What is Sjogrens syndrome associated with?
Loss of tear production
Primary lymphoid organs
Thymus
Bone marrow
What can a B lymphocyte become?
Plasma cell
Which cells are capable of phagocytosis?
Macropage
Basophil
Neutrophil
Monocyte
Which cells are not capable of phagocytosis?
Eosinophils
Which cell types are vital for targeting parasites or organisms too large for phagocytosis?
Mast cells
Basophils
Eosinophils
Which immune system is characterised by the use of immunological memory?
Adaptive
What is the purpose of immunological memory?
Faster responses can be developed if the same antigen is encountered again
What are the two types of responses which form the adaptive immune system?
Cell-mediated response
Humoral response
What mainly controls cell mediated response?
T-lymphocytes
What mainly controls humoral response?
Antibodies formed by B lymphocytes
What can T lymphocytes be subdivided into?
CD4+ T helper lymphocytes
CD8+ cytotoxic T lymphocytes
What can B lymphocytes mature into?
Plasma cells
Memory B cells
What are plasma cells responsible for?
Antibody production
Where do B lymphocytes mature?
In the bone marrow
Where do T lyphocytes mature?
In the thymus gland
TCR
T cell receptor
Where is TCR found?
On T lymphocytes
What is V(D)J recombination?
A process of genetic changes that creates a diverse selection of antigen binding sites within T cell receptors on naïve T lymphocytes
Why is V(D)J recombination helpful?
When T lymphocytes are released from the thymus and encounter an antigen, there will be more chance that the antigen will be recognised by one of the TCR binding sites that have been developed
How are mature B cells activated?
Through binding to the antigen of a pathogen or T helper cell
What is thymopoiesis?
The process in the thymus by which thymocytes differentiate into mature T lymphocytes
What is the primary function of thymocytes?
The generation of T lymphocytes
What processes do thymocytes have to go through in order to be released from the thymus as naïve CD4+ or CD8+ T lymphocytes?
Positive and negative selection
What does positive selection involve?
Selecting T lymphocytes with T cell receptors capable of interacting appropriately with host MHC molecules
What happens if the double positive thymocytes are able to interact with the MHC?
They survive and continue to negative selection
What happens if the double positive thymocytes are unable to interact with the MHC?
They are destroyed by apoptosis
What does negative selection involve?
Identifying thymocytes that interact too strongly with self antigens within the thymus
What happens to thymocytes that react too strongly with self antigens in the thymus during negative selection?
They are destroyed by apoptosis
What happens to thymocytes that survive both positive and negative selection?
They differentiate into single-positive T cells (either CD4+ or CD8+) depending on whether their TCR recognises an MHC class I-presented antigen or an MHC class II-presented antigen
What is the body’s first line of defence?
Physical barrier -skin -mucous membranes Chemical barrier -acid in stomach - enzymes in saliva and lacrimal eye fluid -defensins in skin
What are the first cells at the site of an infection?
Phagocytes - nuetrophils and macrophages
NK cells
What is leukocytosis?
Release of neutrophils from bone marrow into the blood stream
What do mast cells do in the event of injury?
Release histamine which causes vasodilation at the site of injury
What are the main differences between the adaptive and innate immune systems?
Immunological memory Systemic response (adaptive) Specific response (adaptive)
What is the humoral reponse?
Allows the body to achieve immunity by encountering pathogens randomly or on purpose
How does the humoral response work?
Dispatches antibodies to blood and lymph
What is an antigen?
An invader from outside such as a bacterium, virus or fungus, or a toxin/diseased cell from within
Large signalling molecules not normally found in the body
What is required of a B cell before it can be mature?
Immunocompetence
Self-tolerance
Immunocompetence
How to recognise and bind to a particular antigen
Self-tolerance
Knowing not to attack your body’s own cells
What happens to a naive B cell when it is activated by an antigen?
Divides into an “army” of cells with the same antibody
Some become effector B cells,or plasma cells, to fight the antigen, others become memory cells
Why do T cells require professional antigen presenting cells?
They cannot recognise whole antigens
What are professional antigen presenting cells?
Display class II MHC on their surface
Which cells display MHC class I?
All nucleated cells (ie not RBCs), if functioning normally
What are the types of professional antigen presenting cells?
Macrophages
Dendritic cells
B cells
Which class of MHC binds to fragments of exogenous antigens?
Class II
What are the types of T cell?
Helper Cytotoxic Memory Suppressor Natural killer
What are CD8+ T cells?
Cytotoxic T cells (once primed by antigen-presenting cells)
What is the function of a cytotoxic T cell?
Recognizing and destroying virally infected host cells, host cells that have become malignant, or any other host-cells showing signs of damage via their MHC I expression
How do cytotoxic T cells kill a cell?
Release IFN and TNF-α, which have direct anti-viral and anti-tumour effects
Release cytotoxic granules containing perforin and granzyme proteins in the direction of target cells
Induce apoptosis via Fas and FasL interactions with the target cell
Perforin
Produces a pore in the target cell membrane allowing the entry of granzyme enzymes
Granzymes
Proteases that trigger the caspase cascade, which eventually leads to apoptosis of the target cell
Fas and FasL interactions
Activated Tc cell will express FasL on its cell surface. This then binds to the Fas receptor on its target cell. The binding of FasL with Fas results in down-stream effects within the target cell that triggers the caspase cascade, and causes apoptosis
What are CD4+ T cells?
Helper T cells
What is the function of helper T cells?
Help activate other immune cells by releasing T cell cytokines to either stimulate or regulate the immune response (cytotoxic T cells)
Responsible for B lymphocyte antibody class-switching
Responsible for activation and growth of cytotoxic T lymphocytes
Maximize the activity of phagocytes
What is the function of regulatory T cells?
Responsible for suppressing the activation, proliferation and cytokine production of CD4 and CD8 lymphocytes
Control the response to self-antigens, and in this way monitor the process of self-tolerance
Which lymphocytes are responsible for humoral immunity?
B lymphocytes
What is the significance of IgM?
Largest antibodies and form an important part of the primary antibody response to an antigen. As a result of their size and increased number of binding sites, they are much more efficient at activating complement
What is the significance of IgA?
Dimeric and present within secretions such as tears and breast milk
What is the significance of IgG?
Form the main component of the secondary antibody immune response to an antigen, and are the only isotype of antibody able to cross the placenta
What is the significance of IgE?
Form part of the immune response to parasites, however they are also involved in the pathogenesis of allergic reactions
Which is the only antibody able to cross the placenta?
IgG
Opsonins
A molecule that becomes attached to the surface of a microbe to increase the efficiency of phagocytosis
Opsonins can be recognized by surface receptors on neutrophils and macrophages
What is opsonisation?
The process of attaching opsonins, such as IgG or complement proteins, to the surface of pathogens to target them for phagocytosis
Complement
A cascade of proteolytic enzymes that interact with one another and with other molecules in the immune system to generate (for example) inflammatory mediators and opsonins. The common endpoint of the complement cascade is the formation of the membrane attack complex (MAC)
Chemotaxis
The movement of a cell directed by a chemical concentration gradient created by chemokine release
Chemokines
A large family of structurally homologous, low molecular weight cytokines that stimulate leukocyte movement
Pattern Recognition Receptors (PRRs)
Receptors that recognise PAMPs and DAMPs, and thereby activate innate immune responses
PAMPs
Pathogen Associated Molecular Patterns
DAMPs
Damage Associated Molecular Patterns
Which antibody is found in the highest concentration in primary infections?
IgM
Which antibody is found in the highest concentration in secondary infections?
IgG
Changes in which portion of the antibody produces a change in isotype?
Heavy chain
