Introduction to innate immunity Flashcards
What is immunology?
The study of physiological mechanisms that humans and other animals use to defend their bodies from invading organisms.
e.g.
- Bacteria
- Viruses
- Fungi
- Parasites
- Toxins
What are some passive defence mechanisms?
Skin
Mucous membranes
Both first lines of defences. Anatomical and secretory barriers that protect against pathogen entry
What is the first line of defence?
Protection against pathogen entry e.g. skin and mucous membranes
How does skin protect against pathogen entry
Acts as an external barrier
Also have a large variety and diversity of microbes on the skin surface which helps with being a first line of response as they can act on the pathogens before the enter the body.
What are some chemical and bacterial barriers?
Where are they found?
Oral cavity
- Saliva 00> 95% H2O, immunoglobulin A (identifies pathogens), amylase and lipase.
- Bacteria from the oral cavity can resist gastric acid and colonise in intestines
Stomach
- Gastric acid (pH2/3 –> aid digestion and protection)
Intestines
- Variety of microbes
Skin
- Sweat gland (pH5) –> secrete a wide array of antimicrobial peptides which restrain growth of various microbes on the skin
Lungs
- Mucus –> first line of innate defence, provides an essential first host barrier to inhaled pathogens that can prevent pathogen invasion and subsequent infection
Eyes
- Tears –> contains a substance called lysozyme which has antibacterial action and works to prevent invasion and infection by microbes
What is second line innate immunity?
Non-specific responses
- Innate immune cells
- Inflammation
- Complement
- Antimicrobial substances
May take a few days to become activated
What is part of 3rd line adaptive/ acquired immunity?
Specific responses
Specialised lymphocytes
1. B cells –> produce antibodies
2. T Cells –> T Helper cells –> T Killer cells
What are tissue resident cells?
Cells that live close to areas where defence is required, e.g. lungs, gut, eyes, skin
What are immune cells
Stem cells synthesised in the bone marrow
1. Lymphoid stem cells
- T Lymphocyte (thymus)
- B Lymphocyte –> Plasma cell (mature in circulation)
- NK Lymphocyte
- Myeloid stem cells
- Erythrocyte
- Megakaryocyte (blood clotting)
- Monocyte –> macrophage
- Granulocytes
What are mast cells?
Tissue resident cells.
Granules rich in histamine (vasodilator) and heparin.
Key role in inflammation, wound healing and angiogenesis.
Immune tolerance and defence against pathogens.
When the is damage, mast cells release histamine which is a vasodilator which increase blood vessel permeability allow immune cells to move to area of damage from circulation.
Also encourages angiogenesis –> synthesis of new capillaries –> more immune cells can reach infection site.
What are some examples reasons of acute inflammation?
- Allergic reaction
- Chemical irritants
- Infection
- Trauma injury
- Burns
- Laceration, cuts, wounds
- Frostbite
What are some examples of reasons for chronic inflammation?
- Cardiovascular disease
- Neurological disease
- Autoimmune disease
- Rheumatoid arthritis
- Cancer
- Systemic Lupus Erthymatosus
- Fibromyalgia
- Chronic fatigue syndrome
What are dendritic cells?
Innate cells found in nearly all peripheral tissues
Engulfs pathogens via phagocytosis and kills them
Tissue resident cells
Antigen-presenting cells –> when activated they engulf pathogens, then travel through lymphatic system (absorbed into lymphatic vessels, e.g. thymus), where they encounter T-cells.
Connect second line of defence to the third line - can activate third line cells, especially T cells. Present antigen to the cells, where the T cells can then begin adaptive immune response.
Surface protein expression and cytokine production activates T cells for third line of response.
Particularly susceptible by viruses - viral infections can kill these cells and may compromise immune capacity.
What are natural killer cells?
Innate cells
Can be found in the tissue and also the circulation.
The main cells recognising cells that have been infected by viruses e.g. COVID-19.
Useful to recognise tumoural cells
Their activation depends on other innate cells e.g. mast cells and dendritic cells that release cytokines
Once activated they have the capacity to recognise infected cells, they release Granzyme B and Perforin which opens the infected cell’s cell membrane and causing apoptosis.
They also increase the production of cytokines, amplify the innate response which helps with B cells and T cell activation - activate the adaptive immune response
What do natural killer cells produce?
What does that do?
Granzyme B and Perforin –> open the infected cell’s cell membrane and causes apoptosis.
Increase pro-inflammatory cytokine production –> amplifies immune response by activating the adaptive immune response which involves B and T cells.
What are macrophages?
Tissue resident innate cells.
Small quantities in the circulation.
Monocyte (non-mature macrophages) are circulating cells that once they move to the tissue, the express all their organelles and become mature.
Recognise pathogens and induce phagocytosis (engulf pathogen) –> Pseudopodia are receptors that identify antigen –> the site that activate phagocytosis.
Can place some molecule from pathogen into a membrane receptor and travel to lymphatic system/ lymphatic organs to present antigen to adaptive cells (t cells) –> antigen presenting cells.
When active they produce large quantities of free radicals (hydrogen peroxide, nitric oxide) to increase vasodilation and arrival of immune cells to the site. Free radicals such as nitric oxide have anti-microbial capacity, can kill pathogens on their own by destroying their membrane.
