CH16- host immune response to bacterial infections Flashcards
Major cell wall anitgens of bacteria
Gram positive and gram negative
gram positive had what in it?
peptidoglycan, teichoic acid
gram negative has what in it?
LPS, Somatic (O) antigen), Toxic component Lipid A
what happens when LPS directly activates B cells?
To produce IgM antibodies - potent activator of macrophages
What are some other antigens?
Capsular antigen (K- antigen), Fimbra antigen, Flagellar antigen, Exotoxins
What is Capsular antigen?
K antigen like LPS directly activates B cells to produce antibodies IgM
What does Fibra antigen do?
Stop attatchement. messes with the fimbriae
What does flagellar antigen do?
H antigen. antibodies against flagella
What are exotoxins?
Proteins that gram Positive and gram negative bacteria and causes diseases
what are toxoids
derived from exotoxins and induce the formation of antitoxins in the host.
Can extracellular bacteria live long?
cant live long in phagocytes!
Where do extracellular bacteria replicate?
outside the host ( blood Ct, intestinal lumen) attach epithelial surfaces
Extracellular bacteria causes disease by producing?
endotoxins and exotoxins
In innate immunity what do we do with extracellular bacteria?
Phagocytic cells ( neutrophils number 1) eliminate bacteria via phagocytes
complement activation on bacterial surface
Inflammation
IN innate immunity what does the complement activation do?
Complement mediated lysis of bacteria ( gram - negative bacteria)
Opsonization and phagocytosis ( C3b, iC3b, C4b)
What are our inflammation factors in extracellular bacteria?
C5a, C3a, C4a ( induces local mast cell (histamine)
Adaptive immunity of Extracellular parasites consist of what?
Neutralization of bacterial toxins
Opsonization ( IgG) and Fcy receptor -mediated phagocytes
Complementactivation via the classic path way. IgG IgM
Prevention of bacterial adhearence to mucosal surfaces
What is immunity to intracellular bacteria? what does it do?
Cell mediated-
WHere does intracellular bacteria replicate?
inside host cells - macrophages
Antibodies produced during the phase merely indicate exposure to antigen but doesn’t mean?
they have protective immunity!
Innate immunity what do your macrophages secrete?
IL-12 this activates Natural Killer cells
What do Activated NK cells turn on?
IFN-gamma ( this activates macrophages)
Adaptive immunity for intracellular bacteria is principally humoral mediated. True or false?
FALSE cell mediated
for intracellular cell mediated response what cells are involved and what do they do?
CD4 T helper cells respond to MHC class II peptide antigens that come from bacteria.
IL-12 is secreted from macrophages.
The Activated CD4 cell expresses CD40L and secretes IFN gamma, both of which activate macrophages, enhancing the killing of the microbes in the phagolysosoomes.
What are bacterial superantigens?
they are soluble bacteria antigens
Where do superantigens bind?
V beta domain on the TCR ( CDR4) Bind to alpha chain of class II MHC on APCs
what does crosss linkage of Tcell receptor and MHC class II induce?
T cell activation and proliferation
If there is an over production Th Cytokines what can happen and what does it over produce?
Over produced TNF-alpha leads to system toxicity.
How can the bacteria evade host immune responses?
- ) Killing the phagocyte ( secrete leukocidin)
- ) inhibit membrane attachment ( capsule) (sialic acid which resist C3b) ( M protein alters cell surface membrane)
- ) inhibit fusion of lysosomal granules and phagosome
- ) resistance to killing and digestion (cell wall lipids)
- )escape from the phagosome ( Lysterlysine O)
- ) bacteria contains proteases
- ) antigenic variation
- ) gram positive bacteria ( resistant to complement)
What immunity goes with fungal infections?
innate immunity
Who mediates this immunity?
macrophages and neutrophils
what secretes IFN-gamma?
NK cells, Tcells, CD8
What does IFN-gamma do?
go to macrophages and lyse them.
Antibodies produced in response to fungal infections are useful in what?
Serologic diagnosis
