Immune System Flashcards
What are 3 main activities of white blood cells?
Phagocytosis
Inflammation
Cytotoxicity
What is phagocytosis?
The process of a phagocytic cell destroying an organism by engulfing and ingesting it and destroying it intracellularly.
Also how old red blood cells and dying cells from tissue are removed.
What are two main types of phagocytic cell?
Macrophage
Neutrophil
Describe what macrophages are and what they do
Start as monocytes
When enter tissues they mature into macrophages
Found in most tissues
Part of innate response
They have receptors that can distinguish between different pathogens -called toll-like receptor
Monocytes will migrate to infected area and form extra macrophages to aid tissue macrophages. These sometimes called inflammatory macrophages.
They can also present antigens to T cells and initiate inflammation by releasing cytokines that activate other cells
Describe and explain the role of neutrophils
Short life span (1-2 days) compared to macrophages
Most abundant: 55-70% of wbc.
Differentiated from other granular cells as they are multilobed.
Not present in tissues but respond quickly when infection occurs and migrate to site. Neutrophils are first responders.
Highly phagocytic
Contain lysosomes within granule that contain antibactericidal enzymes like lysosyme.
What is inflammation?
The body’s non specific defensive response to tissue damage or injury.
Part of innate system
What can trigger inflammation?
Trauma
Infection by pathogens
Irritation by chemicals
Extreme heat
What are 4 signs of inflammation?
Redness
Pain
Heat
Swelling
What are 3 stages of inflammatory response?
Vasodilation and increased permeability of blood vessels
Movement of phagocytes to the site of infection and entering the tissues
Tissue repair
Describe what happens when injury occurs?
Specialised cells in connective tissue called mast cells release histamine and seretonin
These cause vasodilation and increased permeability
This causes increased blood flow to area -causing heat and redness
It allows fluid from plasma to leak out causing oedema. The increased tissue fluid also increases pressure on nerve endings - hence pain.
Various plasma proteins are activated too - kinins, clotting system, complement system and immunoglobulins.
Kinins increase dilatation
Complement system attract phagocytic cells by chemotaxis (releasing certain chemicals). Also helps the phagocytes attach and engulf - this is called opsonization
Clotting factors activate proteins and produce fibrin which localises infected area and traps invaders
What are natural killer cells and their role?
Type of lymphocyte -part of innate system
Bind to chemical changes on the surfaces of cancer cells and viruses.
Destroy cells by releasing chemicals through the cell membrane
Best known for killing virally infected cells and early signs of cancer
Release cytokines which can enhance response by activating macrophage and dendritic cells
Nk cells brush past cells - they read the mhc 1 receptor which marks cell as self. Cancer cells and infected cells often lose their mhc 1 cells making them a target
What are two types of acquired immunity?
Cell-mediated - T cell lymphocytes
Antibody-mediated - B cell lymphocytes
What is an antigen?
Any substance that can provoke response from adaptive immune system
Usually protein molecules but can be carbs or lipids
Found on surface of pathogens, cancer cells, pollens, foods.
Describe cell-mediated immunity
Mediated by T cell lymphocytes
Produced in bone marrow. Travel to thymus to mature. In this process they learn to recognise body cells
What are 4 types and function of T cell
Cytotoxic T cells - destroy and kill certain abnormal cells. Bind to cell and release enzymes to destroy it. Can also make cells self destruct (apoptosis)
Helper T cell - once activated they act on innate and immune response. Release cytokines to stimulate B cell and cytotoxic T cell. Recruit neutrophils and phagocytic cells to area
Regulatory T cell - suppress the activity of b and T cells to stop immune response once antigen activated or destroyed. Helps prevent over activity of immune system
Memory T cell - part of the immunological memory. Some T cells remain after antigen destroyed. These cells will reactivate quickly if encounter antigen again. Called secondary immune response
What is antibody mediated immunity?
Also called humoral immunity.
Mediated by B cell lymphocytes
Made and mature in bone marrow and then released into blood
B cells have specific surface receptors to antigens and if exposed causes B cells to grow and multiply rapidly.
Two types of cell produced when multiplying. Plasma cells that secrete antibodies, and memory cells.
What are immunoglobulins?
Antibodies
Soluble proteins in blood circulation and found on surface of B cells.
Produced in response to specific antigen. Lock and key.
They bind to epitopes (specific receptors on antigen) an then disable pathogen
What are 5 classes of ig?
IgG IgA IgM IgD IgE
Describe igG
Most abundant 75-80 of total serum ig.
Lowest molecular weight
Can pass through placenta to foetus and gives immunity to newborn infant
Survives longer than other ig in blood
4 subclasses each with slightly diff functions
What are 4 functions of igG?
- Neutralising the antigen - bacterial toxins and preventing some viruses from attaching to body cells
- Activation of system which helps break down foreign cells
- Opsonization - Enhancing phagocytosis by binding with macrophages once antibody connected - therefore making cells more susceptible to phagocytosis
- Agglutination of antigen - clumping together of pathogen to make phagocytosis easier.
Where is igA found?
Saliva l Tears Sweat Breast milk Nasal secretions
Provides localised protection when in secretions.
Breast milk provides protection from gi infection in babies
Describe IgM
Largest Ig in molecular weight
Found in blood and lymph
most predominate Ig in early phase of immune response
Causes agglutination of microbes
Plays important role in activating complement
Describe IgD
Not much is known about this Ig.
Found on surfaces of B cell s- thought to be important in B cell activation
Describe IgE
Less than 0.01% of serum Ig.
Found on surface of mast cells and basophils.
When binds to antigen - mast cells will release histamine - leads to acute inflammatory response - gives signs of allergic reaction e.g. hayfever.
What is difference between primary and secondary immune deficiency?
Primary = rare. Genetic problems affecting one or more components of immune system.
Secondary = acquired, can be related to many factors. eg. age - premature babies have lower level of igG. Malnutrition - if child has protein deficiency. Infections - e.g glandular fever, measles etc will lower immune system. Cancers e.g leukaemia. Drugs eg. steroids. Burns/Major surgery. Protein loss - eg. nephrotic syndrome or severe diarrhoea.
What is primary response to infection?
When immune system first encounters a pathogen.
What is secondary response to infection?
when the immune system encounters pathogen for 2nd or more time
Describe lag phase?
Innate system does first response then ‘lag’ phase as adaptive immune system makes antibodies.
IgM made first with small bits of IgG. But when antigen next encountered the memory cells will produce antibodies very quickly. This time IgG made in much bigger quantities.
What are two types of active immunity?
naturally acquired - after exposure to bacterial or viral infection
Artificaly acquired - through vaccine - organism either attenuated (weakened) or inactivated (killed).
What is passive immunity?
When individual receives antibodies directly and the immune system not activated.
Natural - when mother passes IgG antibodies from placenta to foetus. At birth IgA passes in colostrum and great milk.
Artifically acquired = injection of immune serum.
Describe B cells
Centre of the cell mediated response
Mediate production of antigen specific Immunoglobulin.
What are basophils?
Highly granular mononuclear cell
Less than 1% of leukocytes
Only circulating leukocyte that contain histamine - similar to mast cells (tissue resident counterpart)
Activate when see antigen and undergo rapid degranulation and release their cellular contents
Can also be activated by chemokine and other inflammatory mediators.
What are eosinophils?
Make up 0.5-1% of leukocytes.
Have role in defence against parasites and nematodes (cytotoxic proteins they hold are important for parasite destruction).
Can be damaging as part of allergic disease.
In allergic symptoms = 3-5%.
Have bi-lobed nucleus and granules.
Recruited to site of inflammation and then once activated can release array of inflammatory mediators.
How does T cell recognise antigen?
T cell receptor cannot bind antigen directly.
Needs broken down peptides of antigen ‘presented’ to it by antigen presenting cell (APC). Molecules on APC that do the presenting are called major histocompatibility complex. MHC 1 - presents to cytotoxic T cells. MHC-2 presents to helper T cells.
This is unstable so needs co-receptors - CD4 for helper and CD8 for cytotoxic.
What are 4 components of innate immunity?
- Physical barrier: skin and mucosal surfaces. Keratin makes difficult for microbes to penetrate. Sebum has antimicrobial chemicals.
Orifices have mucous membranes with goblet cells that produce mucus to trap foreign material - Mechanical Barrier: cilia of respiratory tract (move particles away from organs).
Coughing and sneezing - expels pathogens into air
Tears - wash away dirt and organisms - Chemical Barrier:
Body secretions - tears, saliva, sweat, breast milk.
Contain bacterial enzymes like lysosyme or antibodies (like breast milks IgA).
Some like gastric fluid/semen are acidic and inhibit/kill bacteria - Blood cells
What are main groups of lymph nodes?
Cervical nodes - enlarged when URTI Axillary nodes - upper limb infection Tracheobronchial Mesenteric - found between peritoneum layers Inguinal - lower limb infection
What is role of lymphatic system?
- Role in immune system
- Role in maintaining fluid balance
- Role in absorption of fat - fat too large to be absorbed through capillaries so its absorbed through lymphatic capillaries called lacteals.
What is innate immunity?
Immunity we have from birth
First line defence against pathogens
Very fast initial response
Non-specific
What is acquired immunity?
Develops during lifetime when encounter specific pathogen
Where does lymph enter venous system?
Through R and L thoracic ducts going into R and L subclavian veins.
Describe location of thymus gland?
Bilobed gland.
Upper anterior thorax
Just above heart
Fairly large in babies until puberty
Describe location and function of spleen
Left side of abdomen
Behind stomach and below diaphragm
Largest lymph organ
Contains phagocytes and lymphocytes to generate immune response to antigens as blood passes through
It also filters blood. It removes cellular debris and dead RBC
Describe tonsils and function
Small in mucosa around pharynx
Trap bacteria entering nose and throat
What is MALT and GALT?
Mucosa-associated lymphoid tissue and gut-associated.
Includes peters patches (s.intest), appendix and tonsils
Describe function of lymph nodes
Contain macrophages - engulf and destroy foreign organisms
They are sites for rapid production of lymphocytes as part of immune response
2.5cm long, kidney shaped and found in connective tissue.
What are two main layers of lymph node?
Outer cortex - B cell lymphocytes organised in lymphoid follicles with germinal centres. these enlarge and proliferate when antigen encountered
Inner medulla - contain plasma cells secreting antibodies and macrophages.
How does lymph move around lymphatic system?
No pump
Moves through:
1. rhythmic contraction of smooth muscle of lymph vessels
2. muscle contraction in upper and lower limbs
3. pressure changes in thorax when breathing
What is lymph?
mainly Plasma that leaks from blood capillaries after it’s been through tissues.If it didn’t go into lymph then it would accumulate in tissue which = oedema.
What is diGeorge syndrome?
No thymus gland. At risk of infections
Which are primary lymphoid organs?
Where lymphocytes are made.
Yolk sac in foetus until week 8 in utero
Then foetal lier, spleen and bone marrow
At birth = bone marrow - make RBC and wBC
Thymus - matures T cells
What are secondary lymphoid organs?
Where lymphocytes come into contact with pathogens.
Spleen
Lymph nodes
Lymphoid tissue in GI tract (Peyers patches, tonsils), urogenital and respiratory.
What is haemopoiesis?
Making of blood cells
What is route for WBC from stem cell?
Stem cell = common lymphoid precursor or common myeloid precursor
CLP = T cell, B cell and NK cell
CMP = monocyte/macrophage, granulocyte (neutrophil, eosinophil, basophil) and RBC/platelets
What is the complement system?
Array of about 20 types of soluble proteins which assistantships with adaptive immune system to destroy pathogens.
What are dendritic cells?
Antigen presenting cells. The link between innate and adaptive immune systems.
