Immunology Part 1 Flashcards
Give a general definition of the immune system?
A network of specialised cells, tissues and soluble factors that co-operate to kill and eliminate disease-causing pathogens and cancer cells
What are the key features of the immune system?
- Able to specifically identify and respond to ‘non-self’ or ‘abnormal self’
- e.g. pathogens, cancer cells, infected cells and other ‘danger’ signals
- Able to modify the response to deal with different types of pathogens in the most efficient way possible
- Able to actively promote tissue repair & healing
- Able to remember any pathogens it encounters (Immunological Memory)
Where do viruses replicate?
Inside cells
Where are most bacteria located?
Most are extracellular some are intracellular
What issue does parasite infection cause?
They are huge, too big for macrophages to eat.
What happens to the immune system when a pathogen is cleared from the body?
It switches from a pro-inflammatory to anti-inflammatory state.
What is the role of the anti-inflammatory state?
- avoids excessive damage to healthy tissues/cells
- promotes tissue repait and regeneration
What are some common immune over-reactions?
Autoimmune problems
- type 1 diabetes
- rheumatoid arthritis
- psoriases
- multiple sclerosis
- lupus
- IBD
Allergic Reaction
- Hay fever
- eczema
- asthma
- sinusitis
What is a common immune under-reaction?
Cancer
- hepatitis
- HIV
- shingles
- TB
infection
- viruses
- bacteria
- fungi
- parasites
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What are the causes of emergence of new diseases?
Global village
Population growth
Changes in human behaviour
Changes in dynamics of other infections
Loss of natural habitat
Interactions of pathogens with humans
What is the first line of defence against infection?
Physical barriers
Describe the physical barrier (skin)?
Tightly packed, highly keratinised, multilayered cells
Constantly undergo renewal and replacement
What are the important physiological features of skin?
low pH 5.5
low oxygen tension
What is the role of sebaceous glands?
Secrete hydrophobic oils
Lysozyme
Ammonia
Antimicrobial peptides
Where is mucus present as a barrier to infection?
Mucous membrane lines all body cavities that come into contact with the environment
What is the role of mucous?
Traps invading pathogens
What is present in mucous to enhance its defence properties?
- sectetory IgA prevents bacteria and viruses attatching to and penetrating epithelial cells
- contains enzymes: lysozyme, defensins and antimicrobial peptides directly kill invading pathogens. Lactoferrin acts to starve invading bacteria of iron.
What is the role of cilia in mucosal defence?
Trap pathogens and contribute to removal of mucous, assisted by sneezing and coughing.
Describe the role of commensal bacteria?
100 trillion at epithelial surfaces
>500 species
Symbiotic relationship with the host
Describe the functions of commensal bacteria
- production of bactericidins which influence other bacteria
- synthesis of vitamin K, B12
- reduction in pH of large bowel
- Competition for essential nutrients
- production of anti-microbial short chain fatty acids
What can affect the function of commensals?
Malnutrition
Intercurrent infection
Age
What happens after the erradication of commensals?
Organisms rapidly colonise an undefended niche
- oral candidiasis after oral antibiotics
- vaginal candidiases after oreal antibiotics
- C.Diff after IV antibiotics
What kind of medical interventions breach constitutive barriers?
Insertion of ‘hardware’
- IV lines, catheters, NG tubes
Antibiotcs
Anti-acid medication
Nasal decongestants
Anti-bacterial wipes
What is humoural immunity mediated by?
soluble macro-molecules (lipids, proteins) found in extracellular secretions and fluids
What are the two major components of the immune system?
Cells and soluble factors
Name the cells involved in the immune system
- phagocytes
- neutrophils
- monocytes and macrophages
- dendritic cells
- Lymphocytes
- T cells
- B cells
- NK cells
- Mast cells, eosinophils, basophils
Name the soluble (humoral) factors involved in the immune system
Antibodies
Complement system proteins
Cytokines
Acute phase proteins
What are cytokines?
Diverse collection of small proteins and peptides, produced in respons to infection, inflammation and tissue damage
What is the role of cytokines/
Modulate behaviour of cells and coordinate immune system
Describe the characteristics of cytokines?
- Many cytokines have multiple functions
- Different cytokines may have overlapping functions•
- Short half-life
- Can act locally and/or systemically
Name four cytokines and state their function
Interferons: anti-viral activity
Tumour necrosis factor a: a pro-inflammatory cytokine
Chemokines: control and direct cell migration
Interleukins: various functions
What is paracrine siganlling?
Occurs between local cells where the signals elicit quick responses and last only a short period of time
What is endocrine signalling?
Occurs between distant cells and is mediated by hormones and cytokines from specific cells that tracel to target cells, producing a slower, long-lasting response
What is autocrine signalling?
Produces by signalling cells that can also bind to the ligand that is released, which means the signalling cell and the target cell can be the same or similar
What are anitbodies?
Proteins that are produced in response to an antigen and bind specifically to the antigen
What produces antibodies?
Antigen-activated B cells
What is an antigen?
Any substance that can stimulate an immune response
What do antibodies defend against?
Extracellular pathogens, viruses and toxins
What is different about the binding of antigens and antibodies?
Antibodies can bind to only one epitope
Antigens can contain many binding sited for different antibodies
Where are mature B and T cells found?
Circulating in blood, lymph and secondary lymphoid tissue
When to mature B cells and T cells become active?
When they encoutner a pathogen/antigen
What are B cells responsible for?
Production and secretion of antibodies to defend against extracellular pathogens
What are T cells responsible for?
Key role in defence against intracellular pathogens (viruses, mycobacteria)
What are helper T cells?
Key regulators of the immune system
What are cytotoxic T cells?
Kill virally infected body cells
What is the structure of NK cells?
Large granular lymphocytes
What is the role of NK cells?
Can detect and kill tumour cells and virally infected cells
Kill antibody-bound cells/pathogens
Release lytic granules that kill
Where are mast cells found?
Reside in tissues and protect mucosal sufaces
Where are basophils and eosinphils found? How are they recruited?
Circulate in the blood
Recruited to sites of infection by inflammatory signals
How common are basophils and eosinophils?
Low number in non-allergic, healthy people
What happens when mast cells, basophils and eosinophils are activated?
Release chemicals such as
- histamine
- heparin
- pro-inflammatory cytokines
What is the release of chemicals such as histamine, heparin and pro-inflammatory cytokines important for?
Defence against antibody-coated pathogens e.g. parasitic worms
Role in mediating allergic response
Where are complement proteins produced?
In the liver
What do complement proteins circulate as?
Inactive precursor proteins
When do complement proteins become activated? and what happens?
When they enter infected/inflamed tissues
they ezymatically cleace and acticate other downstream complement proteins as a cascade
What are complement proteins important in ?
Promoting inflammation and defense against certain bacterial species
What is the role of phagocytes?
- ingest and kill bacteria and fungi
- ingest and clear debris
- dead and dying apoptotic cells
- immune complexes (antigen/antibody complex)
- sources of cytokines which regulate inflammatory response
Where are phagocytes particularly important?
In the exposed sites
- skin
- epithelial tissues- gut, respiratory tract
fast acting, first line of defence against invading pathogens
- defence against bacteria and dungi
Where are monocytes found?
Circulating in the blood
Migrate into peripheral tissues and differentiate into macrohpages
What are macrophages?
Long-lived tissue resident phagocytes
- kupfer cells (liver)
- alveolar macrophages (lung)
- mesangial cells (kidney)
- microglial cells (nervous system)
What are some of the macrophages roles?
Reduce inflammation
Involved in tissue repair and wound healing
Involved in antigen presentation
What are neutrophils also known as?
Polymorphonuclear cells or PMNs
Where are neutrophils found?
In the blood
Rapidly recruited into inflamed, damaged, and infected tissues
What are the characteristics of neutrophil production?
Produced at a huge rate (50-70% circulating cells)
6hr half life
Where are dendritic cells found?
Present at peripheral tissues in immature state
What is the main function of dendritic cells?
Phagocytose antigens and present antigens on their surface to T cells
What is this cell?
Macrophage
What is this cell?
Neutrophil
Identify this cell?
Dendritic cell
Identify this cell
Monocyte
Identify this cell?
Basophil
