B&I innate immunity Flashcards
Describe the basic concept of innate immunity (3)
- Fixed immune response that does not change
- Immediate/first line of defence
- Cellular/humoral
Describe anatomical and physiological barriers
What are some examples?
(2)
- Protection against bacteria (skin, internal organs)
- Eg. enzymes in saliva and tears, low pH of stomach
What are the 3 main types of pathogens?
What is their defence?
- Viruses - (intracellular, use machinery of host cells to replicate) adaptive cellular immunity
- Bacteria - (extracellular) innate and adaptive immunity
- Protozoa and parasites - cant be engulfed by macrophages and neutrophils, but granulated cells have cytotoxins (basophils, eosinophils, mast cells)
What are the properties of gram positive bacteria?
How can it be killed?
- Lights up with gram stain because they have a thick cell wall as a defence
- Requires phagocytosis, can’t be killed directly by compliment
What are the properties of gram negative bacteria?
How can it be killed?
- Doesn’t light up with gram stain - has thin cell wall surrounded by outer membrane
- Can be lysed directly by compliment
What are the 5 steps in neutrophil extravasation
- Activation (chemokine signals)
- Tethering (counter receptors)
- Adhesion (to capillary wall)
- Diapadesis (extracellular space)
- Chemotaxis (chemokine gradient to infection)
One of the mechanisms to identify bacteria is complement receptors (CR).
What are CR?
How do they work? (2)
What is the main neutrophil receptor?
Myeloid cell receptors that bind activated complement components on bacteria
1. Complement coats bacteria for the complement cascade/phagocytosis
2. Cross linking of surface CR initiates phagocytosis
CR1 is main neutrophil receptor, binds to C3b
One of the mechanisms to identify bacteria is Fc receptors (FcR) AKA “antibody mediate phagocytosis”.
How does this work? (3 steps)
- IgM and IgG antibodies bind to antigens and expose Fc region
- Neutrophil FcR(eceptor) binds to Fc region which activates phagocytosis
- Membrane invaginates, forming a phagosome which fuses with the lysosome and kills
What are the steps in phagocytosis? (3 steps)
consider PAMP and TLR
Phagocyte = macrophages and neutrophils
- Pathogen associated molecular pattern (PAMP) binds with toll-like receptor (TLR) on phagocyte
- Pathogen is engulfed in phagosome, which fuses with lysosome
- Enzymes in lysosome digests pathogen and is removed through exocytosis
What do pattern recognition receptors (PRR) do?
What is the most common PRR?
- Bind complex molecules unique to microbes
- Most common = toll-like receptors (TLR)
What are pathogen associated molecular patterns (PAMP)? (3)
- Molecules unique to microbes recognised by PRR’s
- Structurally complex (lipopolysaccharides) and stable
- “Power switch” for adaptive response
What is a lipopolysaccharide (LPS)? (4)
What is the receptor for LPS?
- A membrane component of all gram NEG bacteria
- Tiny amounts produce powerful innate response
- Pyrogen - causes fever when injected into bloodstream
- Release of LPS by bacterial infections leads to life threatening SEPTIC SHOCK
- TLR4 is the receptor for LPS
What is the function of Fc receptors (FcR) in innate immunity?
They are myeloid cell receptors that bind antibodies, coating a microbe
What causes affinity maturation of B cells? (2)
- It is driven by continued somatic hypermutation of the rearranged Ig gene after the B cell has
encountered its cognate antigen - This is why immunity works
