Bacterial infection- better Flashcards
innate immunity in bacterial infections
- complement
- phagocyte recognition
- phagocyte killing
adaptive immunity in bacterial infections
- CD8
- CD4
- antibodies
innate response is
quick, but low-level
innate recognised
molecules common to bacteria but absent form the host
innate immune uses what to recognise bacteria
Patter recognition receptors to recognise PAMPs
- coded for in germline- limited diversity
Complemement pathways
classical
lectin
alternative
classical pathway
trigger by recognition of Ag-Ab complex (IgG/IgM) via Fc receptors on immune cell
lectin pathway
recognition of microbial surfaces e.g. mannose
alternative
spontaneous- foreign surfaces e.g. LPS
Killing by complement steps
1) recognition of microbial component
2) generates C3
3) C3 convertase covalently bind to cell surface at which complement activation was initiated- confinedto infectious organism
4) C3 convertase breaks down into C3a and C3b
5) C3b binds to microbial surface and forms part of theC5b convertase (C3b/C5), which forms part of the membrane attack complex (MAC
6) Cda causes inflammation
7) MAC- causes pores to form- cell lysis
Which parts of complement form the MAC
mostly C9- C8, C9, C7, C6, C5b
roles of C3a and C5a
bind to their receptors on mast cells and causes degranulation of histamine
C5a
also a chemoattractant
C3b
opsonisation and phagocytosis
C5b9
lysis of microbe
two types of phagocyte killing
Indirect and direct recognition
indirect recognition
bacteria coated with antibodies are recognised by antibody receptor (Fc receptors) or bacteria coated with C3b are recognised by C3b receptors- triggers phagocytosis
direct recognition
PRRs recognising PAMPs e.g. by TLRs
consequence of phacgocyte killing
- activating of pathways leding to cytokine and chemokine productions
- ingestion and killing
TLRS have 2 portions
-extra-cellular and intracellular
extracellular
-ligand recognition
intracellular
signalling
bacteria recognised by TLRs are
ingested and killed by phagocytosis in the phagolysosome
TLR/1/2
peptidoglycan
TLR 4
LPS
TLR3
Ds RNA
TLR 5
flagellin
TLR 7/8
ssRNA
Il-1
activates endothelial cells- fever
IL-6
proliferation of B cells- antibodies
TNF-alpha
activates endothelial cells- fever
activate neutrophils
interferon- alpha
- antiviral immunity (CD4/8)
- used to treat HepB/C
Interferon B
- antiviral
- promotes CD4/8
adaptive immunity recongises
antigens that are unique to individual pathogens
the adaptive response is
slow to develop and mature, but evokes a powerful, long-lasting and remembered response
MHC presentation
dendritic cells (APCs) phagocytose bacteria and process parts of it to be presented on the outside via MHC I/II receptors
MHCI
- markers for CD8 T cell responses- via cytosomal pathways
MHC II
-markers for CD4 T cell response- via endosomal pathways
CD8 T cell responses- cytotoxic- are appropriate when..
bacteria has invaded and grown within the host cell
CD8 t cell responds by
killing host cell using perforins, granzymes and granulysin
examples of infections tackled by CD8 response
TB
Salmonellosis
Listeriosis
Melioidosis
CD4 Tcell secrete which cytokines
Il-17, TNF, IFN-Y,
Il-17 and TNF alpha
inflammation
IFN-Y
macrophage activation and phagocytosis
B cells responses are promoted via
CD4 T cell response via various cytokines e.g. IL-6
Roles of antibodies
-promote complement binding
-agglutination
-neutralising
-opsonising
-
which bacterial diseases require n antibody response
Tetanus Plague Pertussis Streptococcal pneumoniae Meningitis Anthrax
tetanus and anthrax, pertusissis
antibodies neutralise toxins
Plague
antibodies have an unknown role
Pertussis
- neutralising toxin, agglutinating, opsonising, complement activating