16, 17. The Immune System Flashcards
What is the timeline of the innate and adaptive immune systems?
🔸 0-4 hours, Fixed defences of the innate (non specific) immune system
🔸 4-96 hours, Induced defences of the innate immune system
🔸 96 hours, adaptive (specific) response
What is the general process of the removal of an infectious agent?
🔸Infection recognised by phagocytes and soluble components (eg. Lysosomes) of the innate immune system
🔸Recruitment of effect cells (e.g macrophages) of the innate response
🔸 transport of antigen to lymphoid organs, for recognition by T and B cells, and proliferation of these cells
What is a pathogen?
Harmful organisms and viruses
What is immunity?
The ability to avoid disease when invaded by a pathogen
How specific is innate immunity?
🔸 Non specific
🔸 Involves recognising components that are common to many pathogens
🔸 Typically very rapid response
What is the specificity of adaptive immunity?
🔸 Able to distinguish between healthy cells (self) and abnormal cels and molecules that are not self
🔸 Involves recognising components that are specific to each particular pathogen
Where do our immune system cells come from?
BLood cell production
🔸 Multipotent hematopoietic cells in the bone marrow give rise to lymphoid progenitor cells that become B or T lymphocytes
What immune system cells are associated with the innate response?
Macrophage, mast cells, complement proteins
What immune system cells are associated with the adaptive immune responses?
B cells, T cells, antibodies, Th cell, Tc cell
What immune cells are associated with both?
T cells and Natural killer cells
Where do B cells mature?
B cells mature in the bone marrow, then circulate in blood and lymph
Where to T cells mature
Immature T cells migrate from bone marrow to thymus to mature, then circulate in blood and lymph
What is plasma?
🔸Fluid remaining when white blood cells, red blood cells, platelets are removed
🔸Considered the connective tissue of blood
What is the difference between plasma and lymph?
Plasma and lymph have a similar composition but plasma contains both white and red blood cells while lymph contains no red blood cells
What are lymph nodes?
Small round structures at many sites along the lymph vessels and contain white blood cells/leukocytes
As lymph passes through the nodes, it is filtered and inspected for non self molecules/pathogens
How are immune system cells transported?
In the blood and lymphatic system
What are macrophages and what is their function?
They engulf and digest pathogens, cellular debris and pathogen infected cells.
Can move through leaky blood vessels to site of damage
What are mast cells?
Found surrounding blood vessels and nerves in the connective tissue of most organs, and in the boundaries between the internal and external environment
What do macrophages secrete?
Defensins
Nitric oxide
What do mast cells secrete?
Histamine
Prostaglandins
Tutor necrosis factor
What roles do complement proteins carry out?
- Chemotaxis (attracting phagocytes to an injured area
- Attach to antigens on pathogen surface or to an antibody bound to a pathogen, helping phagocytes to recognise and kill pathogens
What does the first line of defence involve?
Skin, mucus, cilia, chemicals (lysosome), flora
What does the second line of defence include?
Phagocytes Complement Interferons Inflammation fever Mast cells
How does injury cause inflammation?
Injury causes histamine release from mast cells which are attracted to the area of injury
What does histamine do when released by mast cells?
🔸Histamine causes vessels to become more permeable (particularly to proteins)
🔸Complement proteins move from blood into the infected area attracting neutrophils and macrophages that move from blood to infected area ad bind to and engulf the pathogen.
🔸 Blood plasma also moves into the infected area causing swelling, leading to inflammation
How do platelets contribute to inflammation?
Platelets from blood release growth factors which stimulates dermis cells to divide and heal the wound
Why is inflammation painful?
Increased pressure of swelling and prostaglandins released from mast cells increase the sensitivity of pain receptors.
Aspirin relieves pain by blocking prostaglandin synthesis
What causes an allergic reaction?
When a non self molecule that is normally harmless binds to mast cells, causing release of histamines, then inflammation and itchy or watery eyes/rashes.
What is an autoimmune disease?
- Immune system fails to distinguish between self and non self and attacks tissues in the body
- Inflammation can be more general and found throughout the body like in rheumatoid arthritis
What is sepsis?
A bacterial infection caused by damage to the body (splinter, cuts on arms or legs, stabbing, burns) does not stay localised to one area and spreads throughout the body and dilation of blood vessels spreads throughout the body.
Causes a drop in blood pressure which is life threatening medical emergency.
How is lymph transported throughout the body?
Lymph is not pumped around like blood. It moves through vessels by body movements (contraction of skeletal muscle for example). Thus showing the importance of exercise
What is oedema caused by?
Mechanisms that interfere with normal fluid balance of plasma, interstitial fluid and lymph flow.
Increased blood flow due to dilation of blood vessels (arterioles) supplying the region of injury.
Paracrine factors like histamine cause increased permeability of the capillaries allowing fluid and blood proteins to move into the interstitial space - oedema
What are the steps for oedema due to inflammation?
Increased capillary permeability due to histamine -> endothelial gaps -> increased capillary permeability to plasma proteins -> decreased protein (oncotic) pressure
-> oedema
What is an antigen?
A molecule that interacts with specific receptors on T cells and B cells
For B cells, the receptor is a membrane bound antibody
What is an antigenic determinant (epitope)?
The specific region on an antigen that is recognised by a specific antibody or T cell receptor
What is the difference between immunogens and antigens?
Immunogens are those substances that trigger a response from the immune system, whereas antigens can be defined as molecules that bind to specific B cell or T cell receptors.
Not all antigens produce an immunogenic response, but all immunogens are antigens
How does the humoral immense response display specificity?
It employs antibodies secreted by plasma cells to target antigens in body fluids. Involves antibodies and B cells
How does the cellular immune response show specificity?
Employs T cells to attack body cells that have been altered by viral infection or mutation or to target antigens that have invaded the body’s cells..
Involves T cells and T cell receptors
What are the parts of an antibody and their function?
the constant region determines the class of antibody molecules
The variable region of the light and heavy chains is where the antigen binds
How is each antibody bivalent?
It has two identical binding sites for antigens that are the same. Antigens bind in the antigen binding region via their antigenic determinants
What are the two types of B cells?
Plasma cells that secrete antibodies (short acting)
Memory cells have membrane bound antibodies (long acting)
What are B cells?
Their membrane bound antibodies bind pathogens then the complex is endocytosed, resulting in activation of memory B cells and production and secretion of more antibodies
What are the two types of T cells
T helper cells
Assist both humoral (b cells) and cellular T cells
The Th cells respond by producing cytokines that direct the action of other cells (B cells, Tc, macrophages)
T cytotoxic cells (Tc)
Respond by releasing perforins that lyse the infected and abnormal cells
What is the structure of a T cell receptor?
- They are glycoproteins, membrane bound receptors
- Made up of 2 polypeptide chains with different amino acid sequences (alpha and beta)
- The variable region of the 2 peptide chains direct specificity of the antigen binding site
Which cells have MHC class I or class II markers?
MHC molecules are found on all cells. Most cells have MHC class I. Macrophages, B cells and Dendritic cells have MHC class II.
Which cells are involved in antigen presenting?
MHC II molecule presents the antigen to the Th cell or MHC I on infected body cell
How does a macrophage function as an antigen presenting cell?
- Macrophage takes up antigen
- Breaks down antigen into fragments
- A class II MHC molecule binds antigen fragment and carries it to the membrane
- Allows the MHC to present antigen to Th cell
How does antibody binding promote phagocytosis?
- Antibodies bind to antigenic determinants on bacteria
- Macrophages have receptors for the constant region of the heave chain of the antibody
- Binding of the antibody to the macrophage receptor activated phagocytosis
What are MHC molecules?
Membrane bound glycoproteins that direct recognition of self from non self
How is the diversity of antibodies created?
There are millions of possible specific antibodies that T cell receptors as a result of the many possible DNA recombination
B and T cells can produce new gene combinations to create millions of different variable regions in antibodies and T cell receptors.
What is clonal selection?
- Antigens presented to the immune system trigger the proliferation of lymphocytes specific for that antigen
- The lymphocytes proliferate and generate a clone of genetically identical cells
What is clonal deletion?
During early differentiation any immature B or T cell that shows potential to mount an immune response against self antigens, undergoes programmed cell death
How does proliferation occur?
Antigen binding and Th cells signalling selects a B cell for proliferation to form a clone (colony) of cells (effector cells) and memory cells
What is the difference between immunisation and vaccination?
Immunisation is exposure to disease causing pathogens which provides natural immunity (memory B and T cells)
Vaccination introduces an attenuated pathogen that does not cause a disease and allows the immune system to create memory B and T cells (artificial immunity)
How does clonal selection create autoimmunity?
Normally during clonal selection immature B cells and T cells that show the potential to trigger an immune response to self antigens undergo apoptosis.
May be caused by failure of clonal deletion or molecular mimicry - self antigens have components that resemble non self and are recognised by T cells
