Innate Immunity Flashcards
Innate Immunity
- 1st line of defence
- more general
- triggers acute inflammation response
- phagocytosis by NFs, macrophages, DCs
Cells that initiate acute inflammation response?
- NFs
- macrophages
- DCs
=> produce cytokines and IFNs
Adaptive Immunity
- more specific
- tailored to pathogen
- long-lasting or protective immunity to host
- found only in vertebrates
Cells connecting innate and adaptive immune system
DCs and macrophages -> act as APCs
- present processed antigens from killed pathogens to adaptive/specific immune system to T-cells
(Th and T cytotoxic)
Innate vs Adaptive
Innate:
- generic receptors (TLRs)
- fast (hours/days)
- no amplification
- short duration
- no self discrimination
Adaptive:
- highly specific (TCRs and BCRs)
- slow (days/wks)
- amplification
- long duration (immunological memory)
- has self discrimination from self antigens and non self
Antigen specific receptors in jawed vertebrates
Adaptive:
- BCRs and TCRs
- Jawless: variable lymphocyte receptors (VLRs)
Innate:
- PRRs (i.e. TLRs)
Primary Lymphoid Organs
- bone marrow (stem cells give rise to all immune cells except T cells)
- thymus (produces T-cells)
Secondary Lymphoid Cells
Lymph nodes
Spleen
(non-circulating immune cells)
Site of haemopoiesis
Primary lymphoid organs (bone marrow, thymus)
Hematopoiesis
The development of major immune cell lineages
What cells develop in bone marrow?
All except T lymphocytes (occur in thymus)
At birth: all bones of the skeleton
By puberty: sternum, vertebrate, iliac bones and ribs
Types of Adaptive Immunity
1) Humoral
2) Cell-mediated
Humoral Immunity
B lymphocytes -> secrete Abs -> eliminate extracellular microbes
Cell-mediated immunity
Helper T cells (CD4+) - cytokines
Cytotoxic T cells (CD8+) - directly kill
(extracellular pathogens)
Immunity to bacteria and fungi
- mainly involves phagocytosis and Abs
Determinants of the defence mechanism against bacteria
- gram +ve - strep pneumonia (lungs)
- gram -ve h.pylori (gastric ulcers) (TB)
- gram +ve -> cell wall is 90% peptidoglycan -> susceptible to lysozyme degradation
- gram -ve -> susceptible to lysis by complement
How are the majority of bacteria killed?
- phagocytosis
-ab mediated opsonization (binding of Fe by lactoferrin)
How can phagocytes detect the presence of bacteria and viruses?
PRRs on their surface
What do PRRs detect?
PAMPS (danger signals)
e.g. TLRs (TLR4 detects LPS (endotoxin))
How do macrophages and DCs recognise bacteria, fungi and viruses?
- PRRs (TLRs)
- mannosyl-fucose receptors -> bind sugars on surface of microbes
- CD14 receptors -> LPS binding protein
- Fc receptors -> bind Abs to pathogen
- Complement receptors (CR1/CD35) -> bind complement coated microbes
Role of Ab
- direct ab neutralization of toxins
- secretory IgA (sIgA) for protection of mucosal surfaces - sIga dimers secreted onto intestinal lumen surface
- opsonisation of bacteria with ab - enhances phagocytosis (NFs and macrophages)
What immune cells express PRRs?
All do but main source is innate
TLRs in endosome
TLR3: dsRNA & ssRNA viruses
TLR7: ssRNA viruses
TLR9: CpG dsDNA
-> mainly found on APCs
RNA Viruses TLRs
- TLR3,7,9
- RLRs (RIG-1 like & MDA5)
- NLRs (NLRP1,2,3)
