Primary Protective Barriers, Recognition of pathogens and Phagocytosis Flashcards
What are the functions of innate immune system?
Prevention- Prevention of access of pathogens to the host
Recognition and response-
1-recruitment of immune cells to the site of the infection via production of chemical mediators.
2- detection and removal of pathogens and foreign substances by specialised leukcytes and the complement.
3- Activation of adaptive immune system via antigen presenting cells.
What are the 3 types of primary protective barriers?
Anatomical (physical) barriers- e.g. skin, mucousal epithelium
Chemical
Commensal microflora
Describe the structure of skin and how does it act as an anatomical barrier and biochemical weapon?
Has 2 layers
Epidermis- outer, thinner layer. Densely packed with dead cells full of waterproof keratin. This layer acts as a barrier to prevent the entry of pathogens
Dermis- Thicker inner layer, Contains connective tissue, blood vessels, sweat and sebaceous (produce fatty substances) glands, macrophages, dedritic and mast cells
Skin as a biochemical weapon-
1- ~ ph of 5.5 (low)- helps prevent the growth of harmful pathogens
2- secretion of antimicrobial peptides and proteins (e.g. proriasin against E.coli) . These peptides act as natural antibiotics, neutralising potential pathogens on the skin surface.
3- fatty acids in sebum produced by sebaceous glands. (These fatty acids have antimicrobial properties)
What is mucosal epithelium and how does it act as a physical barrier?
Mucosal epithelium is made up of epithelial cells that form a protective barrier. It lines the gastrointestinal, respiratory and urogenital tracts.
Mucus production by goblet cells (specialised epithelial cells) prevents pathogens adhesion to the epithelum, making it harder for pathogens to infect the tissues.
In the respiratory tract, cilia moves mucus along the airway to help clear out pathogens
How does mucosal epithelium act as a biochemical weapon?
The mucosal epithelium secretes substances that actively kill or inhibit pathogens such as:
1) Lysosomes- Attacks the cell wall of gram positive bacteria.
2) Defensins (capable of killing bacteria and inhibiting bacterial growth through direct membrane disruptions and inhibition of bacterial cell wall synthesis) Cathelicinds (display antimicrobial properties) and Histatins (group of antimicrobial peptides -found in saliva and possess antifungal properties) secreted by phagocytes
3- Immunoglobulin A- osponisation of bacteria and viruses
Define opsonisation and opsonins
Opsonisation- a process whereby osponins make invading microorganisms visible and more susceptible to phagocytosis.
Osponins are freely circulating molecules such as particular antibodies (IgA) and complement fragments which attach to the surface of the microbes or dead/damaged host cells, thus making them more susceptible to ingestion by phagocytes.
How does lysozyme play a role in innate immunity?
Lysozyme is an enzyme found in tears, saliva and mucus.
It targets peptidoglycan, which is a key structural component of bacterial cell walls.
Lysozyme hydrolyses the B-1,4 glycosidic bonds between N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) in peptidoglycan.
This weakens the bacterial cell wall, leading to osmotic lysis, in gram + bacteria.
After lysozyme disrupts the cell wall, antimicrobial membranes such as denfensins attack the bacterial cell more effectively.
What are the 3 chemical defences of the body?
1- Low pH
~skin 5.5
~vagina 4.5
~stomach 2
2- Bile - produced by the liver and stored in the gall bladder. Contains bile acids such as deoxyholic acid which are particularly effective against bacteria which causes stomach ulcers.
3- Pulmonary Surfactant - composed of 6 lipids and 4 superfactant proteins. Secreted by alveolar epithelial cells
Functions of pulmonary surfactant:
It prevents alveolar collapse during exhalation
Contains collectins that :
1- opsonise pathogens (bacteria and viruses)
2- enhance phagocytosis by macrophages and monocytes.
Define commensal microflora
Commensal microflora competes with pathogens for:
-attachement sites
- nutrients
▪ Support the host by:
* promoting maturation of immune cells → protection from infections
* aiding polysaccharide digestion and absorption of nutrients by host
gut cells
¡ antimicrobial activity against pathogens (e.g. against Staphylococcus
aureus in human breast milk; bacterial fatty acids against Candida albicans)
What do antimicrobial peptides do?
Attack bacteria, fungi and even viruses
- positively charged peptides and proteins up to 60 amino acids e.g. histatins, defensins and cathelicidins
- Disrupt pathogens membrane, inhibit synthesis of DNA, RNA or proteins
