Bio 7C Flashcards
the second line of defence
what is the second line of defence?
a component of the innate immune system and immediate protection against potential pathogens
- comprised of both cellular and non-cellular components
what consists of the cellular components of the second line of defence?
- leukocytes
- mast cells
- eosinophils
- natural killer (NK) cells
what is the role of leukocytes and what are they comprised of?
they are responsible for protecting the body against pathogens and foreign material
- phagocytes
○ Engage in phagocytosis (consume and destroy foreign material, pathogens, or cell debris present in the body by engulfing it through endocytosis)
○ e.g. neutrophils, macrophages, dendritic cells
□ Antigen-presenting cells
® Sub-group of phagocytes that display antigens from consumed pathogens on their surface and interact with the adaptive immune system (by using their MHC Class II markers)
what are macrophages and their role?
they are a type of leukocyte
* Engages in phagocytosis
* Involved in antigen-presenting
* Found throughout the body
* Slower to act, survives one month
* Initiates acute inflammation
Responses by secretion of various cytokines
what are neutrophils and their role?
they are a form of leukocyte
* Engages on phagocytosis
* Most common type of WBC
* Has a flexible membrane so it can squeeze through the capillary cells into tissue
* Short-lived (only survives a few days)
First cells to arrive at infection site in response
what are dendritic cells and their role?
they are a type of leukocyte
* Engages in phagocytosis
* Involved in antigen presenting
Travels through lymph to lymph nodes and present the foreign antigen to the WBC activating in immune response
what is the role of mast cells?
- Found in connective tissue throughout the body
- Degranulate and release histamines in response to injury and allergic reactions
what is the role of eosinophils?
- Large granular leukocyte responsible for the release of toxic chemical mediators (DNase, RNase, protease)
- Target pathogens that are too large to be phagocyted - Degranulate on contact with pathogen (when the release the toxic chemical mediators)
what is the role of natural killer cells?
- Large granulated cells which target both abnormal and virally infected cells through the use of a killer inhibitory receptor and a killer activation receptor
- Killer inhibitory receptor - examines the surface of cells for MHC Class I marker
receptor and a killer activation receptor
- Killer activation receptor - binds to certain molecules which appear on cells undergoing cellular stress (infected or cancerous cells)
what happens to natural killer cells when MHC markers are present/not present
when there are enough MHC class I markers:
- no apoptosis occurs
when MHC class I markers are not detected:
- NK cell released perforins that form a hole in the cell membrane
- NK cell releases granzymes that enter the hole
- Cell undergoes apoptosis
- Macrophages engulf and digest the dying cell
what consists of the non-cellular components of the second line of defence?
- interferons
- complement proteins
- fever
what are interferons and their role?
- Type of cytokine (signalling molecule) that interacts with receptors on neighbouring cells (causes them to undergo changes to make them less susceptible to viral infection)
- Helps to prevent the spread of virus between cells
what are complement proteins and their role?
- In the presence of certain proteins, these proteins begin reacting with each other in a series of reactions (COMPLEMENT CASCADE)
what is a fever and its role?
Temporary increase in body temperature as many pathogens cannot survive at the elevated temperatures created by a fever (also activates certain proteins in the body that bolster the strength of the body’s defences)
- Prolonged fevers can be detrimental to the body due to the additional stress placed on our cells (no longer functioning at their optimal temperatures)
what are the steps of the inflammatory response?
initiation:
- Macrophages situated in the tissue becomes activated and, along with damaged cells, release cytokines
- Mast cells degranulate (releases histamines)
vasodilation:
- Histamines released from the mast cells travel to nearby blood vessels and bind to specific receptors (causes vasodilation - blood vessels widen to increase blood flow to injury site)
- The reason behind swelling, redness, and warmth
- Formation of gaps in the vessel wall to increase its permeability to cells of the immune system
migration:
- Vasodilation and the increased leakiness of blood vessels allow for a number of innate immune system components to leave the bloodstream and enter the site of injury
- Phagocytes (macrophages and neutrophils) are guided by the cytokines secreted by activated macrophages and damaged cells to the site of injury
- They phagocytose pathogens and digest them using enzymes (lysosomes)
- Complement proteins are attracted to pathogens and make it easier for phagocytes to destroy them
- The pus that comes out of an injured area is caused by the increase in blood flow and immune cell activity
- Contains a large amount of dead immune cells and pathogens
- This continues until the site has been cleared of pathogens and debris
