innate immunity - Unit 4 AOS 1 Flashcards
the innate immune system
- Innate immunity is the type of immunity that is present from birth, is fast acting and produces non-specific responses against classes of pathogens. it does not retain memory for future infection.
- It is composed of the first line of defence and the second line of defence
first line of defence
- The first line of defence consists of physical, chemical and microbiological barriers to prevent pathogens from gaining entry to the body. This includes barriers such as intact skin and mucous membranes.
second line of defence
The second line of defence consists of the actions of immune cells and soluble proteins mounting a rapid but non-specific attack against pathogens that gain entry to the body.
physical, chemical and microbiological barriers
physical barriers: a component of the first line of defence that features solid or fluid obstacles that block pathogen entry.
chemical barriers: a component of the first line of defence that features the use of enzymes, toxins, and acids to protect against pathogen invasion
microbiological barriers: a component of the first line of defence in which the presence of normal flora limits the growth of pathogenic bacteria.
physical barriers in plants
- thick bark: acts as an external layer that prevents the entry of pathogens
- The thick, waxy cuticle and outer epidermal cells provide a physical barrier for plants in the same way that skin does in animals
- formation of galls: prevent the spread of infection
- stomata: can close to prevent pathogens from entering
chemical barriers in plants
- toxins that are harmful to pathogens like saponin and defensins which disrupts cell membranes
- enzymes which affect the functioning or development of pathogens like chitinases which have antifungal properties.
physical barriers in animals
- intact skin: provides a surface between external and internal environments, preventing pathogens from entering the body.
- Mucous secretions and/or hairs in the respiratory tract that trap organisms, and cilia that sweep them away from the airways and into the throat where they are swallowed and destroyed by the gastrointestinal tract
chemical barriers in animals
- Tears and saliva contain lysozyme (enzyme) which can destroy cell walls,
stomach acid: destroys pathogens that are swallowed. - The stomach and genitourinary tracts both produce acids in order to create a hostile pH range to pathogens in these regions
- Acidic sweat that destroys pathogens growing on the surface of the body
microbiological barriers on animals
Microbiotic barriers consist of the normal flora (commensals) that line specific cavities (such as the digestive tract) in most animals
By occupying the available space in the intestines, the microbiota prevents the colonisation of these surfaces by pathogenic cells
cells involved in immunity
- There are many different types of white blood cells known as leukocytes that work to protect our body.
- They are found in blood, lymph and other tissues
- The innate leukocytes include natural killer cells (NK cells), mast cells, eosinophils and phagocytic cells (including macrophages, neutrophils and dendritic cells).
phagocytes and phagocytosis
- One of the most important mechanisms conducted by immune cells is the process of phagocytosis, which involves the engulfment and destruction of a pathogen or cellular debris.
phagocytic cell: neutrophils
- the most abundant white blood cell which engulf pathigens via phagocytosis to destroy them. They also release cytokines which aid in cell communcation
phagocytic cell: macrophages
- antigen presenting cells which engulf pathogens via phagocytosis to eliminate them. They present antigens on their MHC II markers to T helper cells to initiate the adaptive immune repose
phagocytic cell: dendritic cell
- antigen presenting cells which engulf pathogens via phagocytosis to eliminate them. they present antigens on their MHC II markers to T helper cells to initiate the adaptive immune response.
natural killer cells
- Natural killer cells are lymphocytes that kill virus-infected cells or cancerous cells through apoptosis, destroying both the cell and any viruses it contains. This prevents the virus or cancer infecting other cells
- They are a type of lymphocyte and have a comparable role to cytotoxic T cells, except that they are non-specific in function
eosinophils
- Eosinophils are granulocytes that assist in defending against larger parasitic agents that are too large to be engulfed by phagocytosis
- they degranulate and release chemicals to destroy pathogens
mast cells
- cells that contain chemicals in granules and when they detect injury to surrounding cells or are stimulated by antigens or allergens, they become activated and
degranulate, releasing histamine and cytokines .
histamine
- leads to increased permeability of blood vessels
- causes vasodilation, increasing blood flow to the injury site
cytokines/interferons
- cytokines are signalling molecules which regulate communication in the immune system.
- When a cell is infected with a virus, it releases a type of cytokine called interferons. These interferons interact with receptors on neighboring cells, causing them to undergo a number of changes that make them less susceptible to viral infection. This helps prevent the virus from spreading between cells
-changes include a making membranes less fluid or inducing transcription of genes which code for antiviral enzymes.
complement proteins
- Complement proteins are proteins that assist other innate immune cells and can destroy bacterial cells by opsonising pathogens, recruiting immune cells or by destroying pathogens by lysis.
actions of complement proteins
Opsonisation - Complement proteins stick on the outside surface of pathogens and make it easier for cells of the immune system, such as phagocytes, to recognise them as foreign
Chemotaxis - Complement proteins gather near a pathogen and attract phagocytes to it, making it more likely to be destroyed.
Lysis - Complement proteins can join together on the surface of pathogens, forming a membrane attack complex (MAC), which creates pores in their membrane. This destroys the pathogen by causing lysis via the sudden influx of fluid into the pathogen, causing it to burst.
inflammation
- The process of inflammation increases blood flow to an injured area, bringing a greater number of immune cells and components to help clear debris and fight pathogens that may have entered the body
steps in the inflammatory response
- initiation: upon injury, macrophages situated in the tissue become activated and along with damages cells, they release cytokines. mast cells degranulate, releasing histamine
- Vasodilation: the histamine causes vasodilation, causing blood vessels to widen increasing blood flow to the site in injury.
- migration: histamine causes increased permeability of blood vessels meaning innate immune system components can enter the site of injury and destroy pathogens.
