Immune System Flashcards
Pathogens
Harmful organisms and viruses that can cause disease.
Immunity
The ability to avoid disease when invaded by a pathogen
Innate immunity
Involves recognising components that are common to many pathogens
• Non-specific
• typically a very rapid response
Adaptive immunity
Involves recognising components that are specific to each particular pathogen
• specific
• can distinguish bw healthy, abnormal and non-self cells
• typically slow to develop and longer lasting
Phagocytosis
Ability to eat/engulf pathogens, apoptotic or necrotic/dead cells.
Examples of cells in innate immunity
- Macrophage
- Complement proteins
- Mast cells
- leucocyte (WBCs)
Examples of cells in adaptive immunity
• B-cell • Antibodies T cells • helper cells • cytotoxic cells
B and T cells are lymphocytes (type of white blood cell)
Formation and development of B and T cells.
B cells develop and mature in the bone marrow.
Then circulate in blood and lymph.
T cells develop in the bone marrow and then migrates to the thymus to develop.
Function of the lymph nodes
- Small, round structures at many sites along the lymph vessels.
- As lymph passes through the nodes, it is filtered and ‘inspected’ for non-self
- contain many WBCs (lymphocytes)
- connected to one another by lymph vessels
Difference between lymph and plasma
- Plasma: contain both white and red blood cells
* Lymph: contains no red blood cells
Macrophages role
Have function in the innate and adaptive immune system
- engulf and digest pathogens, infected cell, cellular debris
- use defensins to kill pathogens after engulfing them
Where are mast cells found?
- Found in surrounding blood vessels and nerves in the connective tissue of most organs
- In the boundaries between the internal and external environment
What do macrophages secrete?
Defensins
- nitric oxide
What do mast cells secrete?
- Histamines
- prostaglandins
- Tumor necrosis factor
What is the complement system?
- Specialised proteins involved in both innate and adaptive immune systems
- more than 20 diff. proteins
- mostly made in the liver
What is the mode of action of complements?
- Chemotaxis - Attract phagocytes to an injured area
- Attach to antigens on pathogen surface or to an antibody bound to a pathogen - this helps phagocytes to recognise and kill pathogens
- lead to lysis (break down) of cells
1st line of defence
Skin, mucus, cilia, chemicals (lysosome), flora.
2nd line of defence
Phagocytes, complement, interferons, inflammation, fever, mast cells.
Why is inflammation painful?
• Increased pressure of prostaglandins released from mast cells - this increases the sensitivity of pain receptors.
Aspirin relieves pain by blocking synthesis of prostaglandins.
Allergic reactions
- non-self molecule that is normally harmless binds to mast cell
- mast cells release histamines
- inflammation causes itchy/watery eyes
Autoimmune disease
Immune system fails to distinguish between self and non-self and attacks tissues in the body
Sepsis
- A bacterial infection caused by damage to body (ie. cut, splinter, wound)
- does not stay localised to one area and spreads throughout the body and dilation of blood vessels also spreads
- this leads to drop in blood pressure - can be lethal
Why is exercise important for the functioning of the immune system?
Lymph is not pumped around like blood, it moves through vessels by body movements. (ie contraction of skeletal muscles).
Lymph also transports dietary fats and lipid-soluble vitamins
What is oedema?
A condition characterised by an excess of watery fluid collecting in the cavities or tissues of the body.
Oedema due to inflammation
- Increased blood flow due to dilation of blood vessels supplying the region of injury
- paracrine factors like histamine cause increases permeability of capillaries
- fluid and blood proteins move to the interstitial space - oedema
Proteins in the adaptive immune system?
- Antibodies (B cells)
- T-cell receptors (T cells)
- MHC
- Cytokines
Function of cytokines and what cells secretes it?
- secreted by T helper cells.
* via specific receptors they activate or inhibit B-cells, macrophages, T-cells
Define antigen
A molecule that interacts with specific receptors on T-cells and B-cells.
• for B cells, receptors is a membrane bound antibody
Define antigenic determinant (epitope)
The specific region on an antigen that is recognised by a specific antibody or T-cell receptor.
• one antigen can have many antigenic determinants
Immunogens
Substances that trigger a response from the immune system
Differentiate between immunogens and antigens
- Not all antigens produce an immunogenic response
* ALL immunogens are antigens
What are 4 key features of the adaptive immune system?
- Specificity
Antibodies and T-cell receptors bind to specific antigens - Ability to distinguish self from non-self (using MHC)
- Diversity
Humans can make millions of different antibodies and T-cell receptors - Immunological memory (memory cells)
Describe the HUMORAL immune response
- response employs antibodies secreted by plasma cells to target antigens in body fluids
- involves antibodies and B cells
Describe the CELLULAR immune response
- 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
How many polypeptide chains make up an antibody?
- 4 chains: 2 light, 2 heavy
What bond holds the light and heavy chain in an antibody?
disulfide bonds
How are antibodies specific?
Light and heavy chains contain variable regions.
Each variable region is specific for ONE antigen.
What does bivalent mean in terms of antibodies?
Each antibody has 2 identical binding sites for antigens that are the same.
- Antigens bind in the antigen binding region via their antigenic determinants
What are the 2 types of B-cells?
- Plasma cells - secrete antibodies (SHORT acting)
2. Memory cells have membrane bound antibodies (LONG acting)
Function of B memory cells?
- their membrane antibodies bind to pathogens
- Complex is then endocytosed
- activation of memory B cells
- production and secretion of more antibodies
What are the 2 types of T cells?
- T-helper cells - assist both humoral and cellular
2. T cytotoxic cells
What do T helper cells do?
T-helper cells respond by producing cytokines that direct the action of other cells (B cells, Tc, macrophages)
What do Tc cells do?
Tc cells respond by releasing perforins that lyse the infected and abonormal cells.
Describe the structure of an MHC molecule.
- made up of 2 polypeptide chains (alpha and beta)
- Variable region of the 2 peptide chains direct specificity of the antigen binding site.
Where are MHC molecules found?
Found on all cells.
- Most cells have MHC class I.
- B cells, macrophages and dendritic cells have MHC class II.
What do Antigen Presenting cells do?
- Macrophage takes up antigen
- Breaks down antigen into fragments
- A class II MHC molecule binds antigen fragment and carries it to the membrane
- MHC ‘presents’ the antigen to a T-helper cell
How does antibody binding promote phagocytosis?
- Antibodies bind to antigenic determinants on bacteria
- Macrophages have receptors for the constant region of the heavy chains of the antibody
- Binding of antibody to macrophage receptor activates phagocytosis
What are MHC molecules?
Membrane bound glycoproteins that direct recognition of self from non-self.
MHC Class I proteins
Found on all nucleated cells
- When a normal cells becomes infected or abnormal, it displays pathogen on MHC class I
- Tc cells recognise cells as non-self
MHC Class II proteins
Found on macrophages, B-cells and dendritic cells
- Present pathogen to Th cells
What is the difference between MHC class I and II?
Class I
- on all nucleated cells
- present antigen to Tc cells
Class II
- macrophages, dendritic, B-cells and APCs
- present to T-helper cells
How is the adaptive immune system diverse?
B and T cells can ‘make’ new gene combinations to create millions of different variable regions in Antibodies and T-cell receptors.
Clonal selection
- Antigens presented to the immune system trigger the proliferation of lymphocytes (T and B)
- Lymphocytes proliferate and generate a clone of genetically identical cells
Clonal deletion
During early differentiation, immature B or T cells that have the potential to cause an immune response agains self-antigens, undergoes programmed cell death.
Formation of memory B cells
- Antigens binding and T-H cell signalling selects a B cell for proliferation
- This B cells forms a colont of effector and memory cells
- Effector cells produce antibodies
Immunisation
- Natural
- Exposure to disease-causing pathogen provides natural immunity (memory B and T cells)
Vaccination
- Artificial
- Introduces an attenuated pathogen that does not cause disease
- immune system forms B and T memory cells
What responses occur after a vaccination?
- primary immune response - number of responding immune cells is low (Vaccine response)
- protective response to pathogen is faster and stronger
Humoral immunity
- Cell with surface antigen
- APC presents antigen to T-H cell
- T-H cell stimulates B cell which either binds to free antigens or produces antibodies
- antibodies either bind to free antigens or to the cells with surface antigen
Cellular immunity
- Cell with surface antigen
- APC presents antigen to T-H cell
- T-H cell stimulates Tc cell to kill all cells with foreign antigens
First and second line of defence action
1st: 0-4 hours
- infection recognised by phagocytes
2nd: 4-96 hours
- Recruitment of effector cells (e.g. macrophages)
Both involve the innate immune system
3rd line of defence action
96- hours
- Adaptive immunity
- Transport of antigens to lymphoid organs, for recognition by T and B cells and proliferation of these cells
