3 - Innate and Acquired Immune System Flashcards
Functions of innate system
- Initial defence against microbes
- Eliminates damaged cells + initiates repair
- Stimulates adaptive immune response
Describe the chemical defence of the innate system
antibacterial peptides
- Small amino acids cationic with anti-microbial activity
- Defensins: kill a wide range of bacteria within minutes
- Secreted by neutrophils, disrupting membranes to form pores resulting in lysis
Describe the purpose of inflammation response by innate immunity
- Triggered by cellular injury
- Attempts to prevent spread of agent
- Dispose debris and pathogens
- Tissue repair
What are the signs of inflammation?
Redness, heat, swelling, pain + loss of function
Describe the pathway of an inflammatory response
injury
release of inflammatory mediators
acute inflammation: removal of damaging stimulus
cells regenerate or heal by scar formation
Provide examples of inflammatory mediators
- Cytokines
- Proteins released by cells that affect other cells - Chemokines
- Proteins released by cells that attract other cells to the area - Acute-phase proteins
- Plasma proteins that increase in concentration due to inflammation within minutes
Describe phagocytosis
Microbes and killed and removed
- Phagocytic cell recognises surface of microbe -> adheres -> ingests
- Held within phagosome, fusing with a lysosome to form phagolysosome
- Exocytosis removes microbe debris
What are the toxic substances that kill and degrade mircobes in phagocytosis?
- Nitric oxide
- Superoxide anions
- Hydrogen peroxide
Describe NK cells
- Eliminates virally infected and cancer cells
- Recognises reduced MHC class I via activating + inhibitory receptors
- Direct cytotoxicity by release of perforin + granzymes
What does ADCC stand for?
Antibody dependent cell mediated cytotoxicity
What is ADCC?
NK cells are able to attach to antibodies on surface of cells via Fc receptor
Describe the missing self hypothesis
- When inhibitory receptor is engaged, the NK cell is not activated -> no cell killing
- When the inhibitory receptor is not engaged, the NK cell is activated -> infected cell is killed
What are the two ways the innate system is stimulated?
PAMPs - Pathogen associated molecular patterns
DAMPs - Damage associated molecular patterns
How does PAMPs work to stimulate the innate system?
Different structures on different pathogens are recognised by cells of the innate system
How does DAMPs work to stimulate the innate system?
Molecules released from damaged cells
- endogenous
- released in response to trauma
- healthy cells are able to release alarmins in response to infection to enhance innate response
What are the receptors of the innate system?
Pattern recognition receptors: cellular phagocytes and soluble molecules
How do cellular phagocytes work as receptors?
Bind to PAMPs/DAMPs to activate signal transduction pathway
promoting inflammation + antimicrobial activity
How do soluble molecules work as receptors ?
Enhances phagocytosis
Active extracellular killing
found in the blood and ecf
Give an example of a cellular PRR
Toll like receptors (TLR)
Where are toll like receptors found?
TLR 1,2,4,5,6,10,11 found on plasma membrane
TLR 3,7,8,9 found on endosome -> viral infections
Give an example of soluble PRR
Pentraxins
Found on plasma
e.g. c-reactive protein
Describe NOD like receptors
Specific for intracellular pathogens
In cytosol
Activated by peptidoglycan, RNA, toxins, flagellin
releases pro-inflammatory cytokines
What are interferons?
inflammatory mediators
broad spectrum antiviral agents
What are the interferon groups?
IFNA: for viral infection
IFNb: for viral infection
IFNy: for inflammatory
How do interferons work?
Bind to specific receptors of neighbouring cells
- neighbouring cells produce protein kinase R
- limiting spread of viral infections to stop production of protein in a cell
- stimulates endonuclease production which degrades viral mRNA
Describe antigen presenting cells
- cells that phagocytise infectious invader
- migrate to lymph node
- digest + present bits of antigen to T-helper cells
- types: dendritic cells + macrophages
Describe humoral immunity
- Antibody mediated
- Acts against extracellular invaders
- Produced by B lymphocytes
What is the action of antibodies in humoral immunity?
- Activate complement
- Trigger phagocytosis
- Neutralise viruses + toxins
- Aggulutination
Describe cell mediated immunity
- Lymphocytes directly/indirectly kill infected cells
- Act against intracellular invaders (viruses + mycobacteria)
- Cytotoxic T cells
What are the classes of antibodies?
IgG, IgA, IgM, IgE, IgD
Primary response
Lag of several days as B cells proliferate
aby levels peak + fall as ag is removed
Aby is predominantly IgM
Secondary response
Second exposure to same antigen Quicker + larger response Rapid rise in aby levels + lasts longer Memory cells have fewer cycles to become plasma cells Aby is predom. IgG
Describe clonal selection
Ag only binds to specific aby
- specific antigen binds to region of b-cell surface aby
- b cell is stimulated
- clone is selected
Describe cytotoxic T cells
- require T-helper cells
- wide range of surface receptors against ag
- each Tc is specific for one receptor
- infected cell express ag on their surface via MHC I
- Tc via T-cell receptor binds + destorys cells expressed the specific ag
- kill by release of toxins -> lysis -> initiate apoptosis
