Lecture 6 - The Immune System Flashcards
What is the structure and function of the Lymphatic system?
- Lymphatic tissue/ organs and cells
- Bone Marrow
- Lymph - fluid similar to plasma
- Lymphatic vessels - carry lymph from periphery to venous system
Protects us against disease
Lymphoid cells respond to environmental pathogens, toxins and abnormal body cells
It produces lymphocytes
Returns fluid to blood
Distributes hormones to circulation
What are the pathogens that cause disease?
Viruses e.g. Epstein Barr
Fungi e.g. Candidiasis
Bacteria e.g. E.coli
Parasites e.g. Schistosome
Outline the production and distribution of lymphocytes
Production occurs in the lymphoid tissues, lymphoid organs and the red bone marrow
Distribution - travels through the lymphatic vessels and capillaries detects a problem and travels to the site of infection
What are lymphatic vessels and capillaries?
Vessels begin as capillaries which are closed on one end and are located between cells of many tissues
Capillaries merge to form lymphatic vessels which have thin walls and lots of valves to prevent backflow
What is the difference between a lymphatic vessels and blood capillaries?
Start as blind pockets rather than tubes
Have a larger diameter
Have thinner walls
Flat or irregular in section
Outline the lymph trunks and ducts
From the lymphatic vessels, lymph passes through the lymph nodes and then into lymph trunks
These include the lumbar, intestinal, bronchomediastinal, subclavian and jugular trunks
Lymph trunks then merge to form either the thoracic duct or the right lymphatic duct
What are the circulating lymphocytes?
T cells - thymus dependent
B cells - bone marrow derived
NK cells - Natural Killer cells - also bone marrow derived
How are lymphocytes produced and distributed?
In the red bone marrow, hemocytoblasts divide to form lymphoid stem cells these can either convert to B cells and NK cells or migrate to the thymus to produce T cells which are then transported to the circulatory system
What are the primary lymphatic organs?
Where immune cells become immunocompetent
Red bone marrow and the thymus
What are the secondary lymphatic organs?
Lymph nodes
Spleen
Lymphoid nodules
Outline the structure of the lymph node
Afferent lymphatic vessels enter then lymph moves through the subcapsular space which contains macrophages to the outer cortex - B cells within germinal centers
Deep cortex - T cells
Core - B cells and plasma cells - medullary cords organise these
Into the hilum and efferent lymphatics
What is the difference between lymph organs and lymphoid nodules?
Lymph organs are separated from surrounding tissues by a fibrous capsule
Whereas lymphoid nodules are a bundle of lymphoid tissue without the fibrous capsule
Outline the flow of lymph
Interstitial fluid
Lymph capillaries
Lymph vessels
Lymph trunks
Lymph ducts
Subclavian veins
What is the function of the lymph node?
A filter which purifies lymph before return to venous circulation
Removes debris, pathogens, 99% of antigens
Outline the distribution of lymph nodes
Gut, trachea, lungs and thoracic duct protect against pathogens in digestive and respiratory systems
Glands - Large lymph nodes at the groin and base of neck - swell in response to inflammation
Lymphadenopathy - Chronic or excessive enlargement of lymph nodes may be due to cancer
What is the difference between non specific immunity and specific immunity?
Non specific (innate) - Block or attack any potential pathogen, present from birth, no memory
Specific (adaptive) - identify, attack and develop immunity to a specific antigen, acquired in response to antigens
What are the 7 methods of non specific defense?
Physical barriers
Phagocytic cells
Immunological surveillance (NK cells)
Interferons (antiviral)
Complement system
Inflammation
Fever
Outline the method of physical barriers?
Eyes - washing with tears, lysozymes
Skin - Anatomic barrier sweat and sebum, antimicrobial secretion, low pH, commensal microbes
Respiratory tract - mucus, cilia, antibody, phagocytosis
Digestive tract - Stomach acidity, normal flora, intestine - alkaline pH, mechanical flushing, enzymes, bacteriocins
Genitourinary tract - washing by urine, vaginal lactic acid
Outline the method of phagocytosis and antigen presentation
Pathogen phagocytised by antigen presenting cell
Lysosome action produces antigenic fragments
ER produces Class 2 MHC proteins which are bound to antigenic fragments these are they displayed on the cell membrane
What are the classes of phagocytes?
Microphages - Neutrophils and eosinphils, leave the bloodstream, enter peripheral tissues to fight infections
Macrophages - Large phagocytic cells derived from monocytes, distributed throughout the body, make up monocyte-macrophage system, may be free or fixed
What are activated macrophages?
Respond to pathogens in several ways
Engulf pathogen and destroy it with lysosomal enzymes
Bind to pathogen so other cells can destroy it
Destroy pathogen by releasing toxic chemicals into interstitial fluid
Outline the method of immunological surveillance by NK cells
Recognition and adhesion of NK cell to abnormal cell
Realignment of golgi apparatus
Secretion of perforin
Lysis of abnormal cell
What are interferons?
Non specific response to viral infections
Proteins (cytokines) - released by activated lymphocytes and macrophages
Slow the spread of disease
What are the 3 types of interferons?
Alpha interferons- Produced by leukocytes, stimulate NK cells
Beta interferons - Secreted by fibrocytes, slow inflammation
Gamma interferons - Secreted by T cells and NK cells, stimulate macrophage activity
What is the complement system?
Enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism
11 Complement proteins C1 to C11
Complement antibody action
A chain reaction
2 paths of activation
Classical (fast) and alternative (slow)
Conversion of inactive protein C3 to active C3b
Forms pores in bacterial cell wall know as the membrane attack complex leads to the destruction of bacteria
What are the effects of complement activation?
Attraction of phagocytes
Enhancement of phagocytosis by opsonisation
Stimulation of inflammation
Destruction of target cell membrane
Outline the method of inflammation and tissue repair?
Response to tissue damage
Increased blood flow - mast cells release histamine
Phagocytes move to the site
Neutrophils remove debris
Clot forms
Fibrinogen is activated
Tissue is repair
Outline the role of fever
Increase in body temperature due to the release of pyrogens - causes the hypothalamus to raise body temp
1. Mobilises defences
2. Accelerates repair
3. Inhibits pathogens
How do mature T cells aid the cell mediated immunity?
They form Helper T cells and Cytotoxic T cells
Helper T cells are cloned and can activate B cells and Cytotoxic cells
Cytotoxic T cells - leave the lymphatic tissue to attack invading antigens
How do mature B cells aid antibody mediated immunity?
They form B cell clones which form plasma cells and memory cells allowing antibodies to be produced
What are the main 2 divisions of specificity immunity?
Cell mediated - T cells - Only recognise fragments of antigenic proteins that are processed in a certain way
Humoral - B cells - Can recognise and bind to antigens in lymph, interstitial fluid or plasma
What are MHC proteins?
Used to distinguish self and non self
Class 1 - On all nucleated cells
Class 2 - On antigen presenting cells and lymphocytes
How does the body recognise infection?
Free living - exogenous
Inside host cells - endogenous
Self antigens are expressed whereas non self are presented
What is central tolerance?
Lymphocytes are exposed to self antigens during development and are deleted if they are specific for self antigens
What is the difference between antigen expression and presentation?
Antigen expression via class 1 MHC proteins on cell membrane of infected somatic cells
Antigen presentation - via class 2 MHC proteins on the cells involved with specific immunity
What are the 3 main types of T cell?
Cytotoxic T cells - cell mediated immunity destroy virally infected cells
Helper T cells - Stimulate function of T cells and B cells
Suppressor T cells - Inhibits function of T cells and B cells
How is a helper T cell and a cytotoxic T cell activated?
APC co-stimulates the inactive T helper cell
The TCR on the T cell binds to the antigen of the APC
This activates it and it is then clonally selected which forms helper T cell clones
Whereas a cytotoxic T cell binds to the antigen of an infected body cell
What is the structure of an antibody?
2 heavy chains and 2 light chains
Disulfide bond
Variable region which differs from antibody to antibody
And an antigen binding site
What are the 5 types of antibody?
IgG - 80% of all antibodies
IgA - glandular secretions
IgM - found in lymph and blood, pentamers, first to be secreted by plasma cells after initial exposure to to antigen - cause agglutination and lysis of microbes
IgD - involved in activation of B cells
IgE - mast cells and basophils - allergic reactions
How are B cells activated and clonally selected?
B cell recognises unprocessed antigen
What is the primary vs secondary response?
Primary response is when the body receives a pathogen for the first time which takes longer to secrete antibodies
Yet as memory cells are produced when the pathogen re enters IgG is released quickly and the pathogen is destroyed
What are the forms of immunity?
Innate immunity - genetically determined
Acquired immunity - prior exposure to antibody
Active immunity - antibodies that form in response to antigens can be induced active immunity ( vaccine) or Naturally acquired
Passive immunity - Transfer of antibodies -Natural - from mother’s breast milk or induced - vaccine
What are the problems with the immune system?
Allergy - overly reactive to a substance that is tolerated by others - high levels of IgE
Autoimmune disease - Immune system doesn’t display self tolerance so attacks self
Transplant rejection - body recognises transplant as non self
Diseases - primary e.g. SCID and secondary
