Changes

LPS is a component of some Gram-negative bacterial cell walls and its recognition is thought to be an ancient mechanism that evolved before the acquired immune system. When released by bacteria, LPS can bind to soluble CD14, which causes the release of TNF-alpha and IL-1 (both lead to systemic phagocyte activation), or to lipoprotein particles, which neutralize it.

LPS is a component of some Gram-negative bacterial cell walls and its recognition is thought to be an ancient mechanism that evolved before the acquired immune system. When released by bacteria, LPS can bind to soluble CD14, which causes the release of TNF-alpha and IL-1 (both lead to systemic phagocyte activation), or to lipoprotein particles, which neutralize it.

===Complement===

====Complement====

Some bacteria, particularly those with an outer lipid bilayer (i.e. Gram-negative), are susceptible to [[Complement]] activated via the alternative pathway (the lytic complex: C5b-9). The release of C3a and C5a lead to histamine release, and attracts and activates [[Neutrophils|neutrophils]]. Components of C3 aid opsonisation of the bacteria.

Some bacteria, particularly those with an outer lipid bilayer (i.e. Gram-negative), are susceptible to [[Complement]] activated via the alternative pathway (the lytic complex: C5b-9). The release of C3a and C5a lead to histamine release, and attracts and activates [[Neutrophils|neutrophils]]. Components of C3 aid opsonisation of the bacteria.

===Phagocytosis===

====Phagocytosis====

Most bacteria are killed this way. [[Complement products]], bacterial components (e.g. f-Met-Leu-Phe) and locally released cytokines are chemotactic for phagocytes. The binding of the phagocyte can be mediated by the following:

Most bacteria are killed this way. [[Complement products]], bacterial components (e.g. f-Met-Leu-Phe) and locally released cytokines are chemotactic for phagocytes. The binding of the phagocyte can be mediated by the following:**Lectins on the bacteria, e.g. mannose-binding lectin of E. coli.

**Lectins on the bacteria, e.g. mannose-binding lectin of E. coli.

**Lectins on the phagocyte, e.g. complement receptors such as CR3.

**Lectins on the phagocyte, e.g. complement receptors such as CR3.

**[[Complement]] deposited on the organism, both classic and alternative pathways.

**[[Complement]] deposited on the organism, both classic and alternative pathways.

==Evading immune defences==[[Image:S aureus.jpg|thumb|right|100px|'''S. aureus''' Brian0918 2006, WikiMedia Commons]]

==Evading immune defences==[[Image:S aureus.jpg|thumb|right|100px|'''S. aureus''' Brian0918 2006, WikiMedia Commons]]

Bacteria can avoid the [[Complement|complement]] reponse in the following ways;

Bacteria can avoid the [[Complement|complement]] reponse. Proteins can be expressed on the surface that divert the lytic complex from the cell membrane; The outer membrane can resist the lytic complex; Some bacteria have an outer membrane that inhibits complement activation and An enzyme found on the membrane of some bacteria is able to degrade complement.

**Proteins can be expressed on the surface that divert the lytic complex from the cell membrane

 

**The outer membrane can resist the lytic complex

Many can also avoid the phagocytic response by secreting repellants or toxins, some bacteria can inhibit [http://www.cellsalive.com/chemotx.htm| chemotaxis]. Once ingested, some bacteria inhibit lysosome fusion or proton pump action (preventing the phagocyte pH from falling), e.g. [[Mycobacterium tuberculosis|M. tuberculosis]]. Some bacteria have outer coats that inhibit phagocyte attachment and some secrete catalase which breaks down hydrogen peroxide. The release of a phenolic glycolipid by M. leprae prevents damage by free radicals. Lipoarabinomannan, released by some [[:Category:Mycobacterium|Mycobacteria]], blocks [[Macrophage|macrophage]] response to IFN-γ and infected cells can lose their ability to present antigens.

**Some bacteria have an outer membrane that inhibits complement activation

**An enzyme found on the membrane of some bacteria is able to degrade complement

*Many can also avoid the phagocytic response:

**By secreting repellants or toxins, some bacteria can inhibit [http://www.cellsalive.com/chemotx.htm| chemotaxis]

**Once ingested, some bacteria inhibit lysosome fusion or proton pump action (preventing the phagocyte pH from falling), e.g. M. tuberculosis

**Some have outer coats that inhibit phagocyte attachment  

**Some secrete catalase which breaks down hydrogen peroxide

**The release of a phenolic glycolipid by M. leprae prevents damage by free radicals

**Lipoarabinomannan, released by some Mycobacteria, blocks macrophage response to IFN-γ

**Infected cells can lose their ability to present antigens

<big>'''Also see [[Innate Immunity to Bacteria]] and [[Adaptive Immunity to Bacteria]]'''</big>

<big>'''Also see [[Innate Immunity to Bacteria]] and [[Adaptive Immunity to Bacteria]]'''</big>

[[Category:To Do - AimeeHicks]]

[[Category:To Do - AimeeHicks]]