Innate Immunity Flashcards
What are the different types of pathogens ?
- bacteria
- fungi
- protists e.g. parasite
- viruses
What are the different ways in which pathogens can enter the body ?
- breaks in the skin
- lungs
- digestive tract
- urogenital system
What is the largest organ of the body ?
The skin
How can pathogens move around the body ?
Via the circulatory system or the lymphatic system
What are the 2 phases of innate immunity ?
1) innate phase
2) early-induced phase
Describe the innate phase of innate immunity
- immediate action
- preformed mediators kill and weaken pathogens
Describe the early-induced phase of innate immunity
- sensing of threat
- recruitment of cells and mediators
- inflammation
What are some of the physical barriers of the immune system ?
- skin
- mucus
- epithelia
- stomach
What are some of the chemical barriers of the immune system ?
- coughing and sneezing
- the body creates hostile environments for pathogens to survive e.g. stomach acid and urine
How do pathogens exit the body ?
The flow of bodily fluids such as urine will cause pathogens to exit the body
What is found in tears and sweat that helps the breakdown of pathogens ?
Lysozyme enzymes in tears and sweat help to dissolve bacterial cell walls
What covers all body surfaces ?
Epithelial cells
Describe how microbes are removed from the skin
There is a longitudinal flow of air and fluid across the surface of the skin to remove microbes from the surface of the skin
Describe the structure of skin
- it is made up of multiple layers of epithelial cells
- the dead outer layer of keratinised epithelium is constantly shedding and so any microbes present are shed
- the skin contains :
• lamella bodies of fatty acids which create a waterproof barrier
• alpha and best defending which create the body’s own anti microbial
• S100 proteins e.g. psoriasin and calprotectin which target any pathogens which could breach the outermost layer
Describe how the stomach is involved in the removal of pathogens
- has a low pH which creates a relatively sterile environment
- contains digestive enzymes which digest microbial proteins and degrade them
- muscular contractions move fluid in and out creating a mechanical flow
Describe how the small intestine is involved in the breakdown and removal of pathogens
- it has a slightly pH than the stomach which means the antimicrobial peptides can work better
- contains digestive enzymes
- the flow of fluid will flush organisms out
Describe how the large intestine is involved in the breakdown and removal of pathogens
- the stable microbiome produces its own antibiotics
- the expulsion of faeces removes pathogens
What is the importance of the flow of fluid from the stomach to the large intestine ?
It prevents microbes from settling and colonising in the body
Describe how pathogens are broken down and removed from the airways
- there is mechanical flow of air in the lungs through coughing and sneezing
- the coordinated movement of cilia in the mucociliary escalator will move mucus and foreign particles up the airway
- alveolar macrophages perform phagocytosis of pathogens
- surfactant proteins such as SP-A and SP-D aid the alveolar macrophages by marking pathogens
What is the function of antimicrobial peptides and mucins ?
They provide a protective barrier against pathogens
How do glands protect against pathogens ?
- lacrimal glands produce tears and these contain lysozymes
- salivary glands produce saliva, lactoferrin, lysozymes and antibodies
- mammary glands produce calprotectin, lactoferrin and antibodies
Describe the function of epithelial cells in protecting against pathogens
Epithelial cells are tightly packed together by tight junctions, adherens junctions and desmosomes providing a strong barrier against pathogens
How do epithelial cells protect against pathogens ?
- epithelial cells are synthetic and produce a range of antimicrobial peptides, mucins and soluble mediators e.g. cytokines and chemokines
- they are involved in the recruitment of leukocytes from the blood to sites of infection and inflammation
- they use PAMP receptors to detect sites of microbes
Why is the cellular response of the innate response activated ?
When the physical and chemical barriers of the innate response are breached the cellular response will be activated
Which cells are the main cells involved in the cellular innate response ?
- the granulocytes of the myeloid lineage of haematopoietic stem cells : neutrophils, eosinophils, basophils and mast cells
- natural killer cells of the lymphoid lineage
Describe the function of neutrophils
- more than 60% of blood leukocytes are neutrophils
- they are recruited to tissues after receiving signals from the inflammatory response
- they carry out phagocytosis
- if infected by fungi and bacteria there will be high levels of neutrophils in the blood
Describe the function of eosinophils
- less than 5% of blood leukocytes are eosinophils
- they are tissue resident cells and maintain tissue homeostasis
- they defend against parasites
- they are involved in the allergy response
Describe the function of basophils
- less than 1% of blood leukocytes are basophils
- defend against parasites
- they are involved in regulating the immune system
What do the granules of neutrophils contain ?
- mostly contain enzymes and other substances used to disrupt pathogens
- lysozymes
- lactoferrin
What do the granules of eosinophils contain ?
- preformed proteins
- cytokines
- chemokines
- growth factors
What do the granules of basophils contain ?
- preformed proteins
- cytokines
- chemokines
- growth factors
- active mediators e.g. histamine
Describe how neutrophils work
1) neutrophils are recruited to the site of infection by chemokine trail
2) once they are in the tissue they carry out phagocytosis
Describe how eosinophils work
- they release their granular components into the surrounding area
- maintain homeostasis in the intestines, uterus, lungs and thymus
What are the 4 ways in which eosinophils release their granules ?
- classical exocytosis
- compound exocytosis
- piecemeal degranulation
- cytolysis
Describe the function of mast cells
- they are tissue resident cells
- they are granulocytes and when activated release their granules in the surrounding area
- they are not polymorphonuclear
- they release active mediators e.g. histamine
- initiate the inflammatory response
Describe the function of monocytes
- they are blood born and make up 2-10% of blood leukocytes
- their main roles are phagocytosis and bacterial killing in blood
Describe the function of macrophages
- macrophages are differentiated monocytes
- they can either be tissue resident or inflammatory
- tissue resident macrophages populate almost every tissue in the body
- inflammatory macrophages undergo changes in size, phagocytic ability, complexity of organelles and hydrolytic enzymes as they enter tissues
Describe the function of dendritic cells
- they are tissue resident cells
- make up a tiny percentage of blood
- act as guardians at potential entry points for microbes
- carry out phagocytosis and do antigen presentation
- link the innate and adaptive immune system
Describe the function of natural killer cells
- large granular cells that target virally infected or cancer cells
- make up 5-10% of circulating lymphocytes
- release cytotoxic chemicals when in cell to cell contact
- have immunoregulatory effects
Describe now natural killer cells work
- if there is a balance of activation and inhibition signals then nothing will happen and the natural killer cell will dissociate
- if the inhibitory signal is lost :
1) the natural killer cell is activated
2) cytokines are released
3) perforin is released
4) cytolysis of infected cells
Describe the function of innate lymphoid cells
- have 3 main families : ILC1, 2 and 3
- have a role in barrier homeostasis
- implicated in barrier disorders e.g. eczema
