Changes

* There are two triggers for the classical pathway of complement activation.

* There are two triggers for the classical pathway of complement activation.

*# '''The binding of antibody to antigen'''.

 

*#* Only IgM and certain IgG subclasses can activate complement this way.

====The binding of antibody to antigen===

*#* Immune complexes trigger complement activation by binding C1.

*#**  C1 cross-links two antibody molecules.  

* Only IgM and certain IgG subclasses can activate complement this way.

*#**  C1 is a complex of:

# Immune complexes trigger complement activation by binding C1.

*#*** C1q

#*  C1 cross-links two antibody molecules.  

*#**** Looks like a bunch of 6 tulips.

#*  C1 is a complex of:

*#**** Each "flower" consists of a globular protein head and a collagen "stem".  

#** C1q

*#**** At least two C1q globular heads must bind to antibody before the complement cascade is triggered.

#*** Looks like a bunch of 6 tulips.

*#*** C1r

#*** Each "flower" consists of a globular protein head and a collagen "stem".  

*#*** C1s.  

#*** At least two C1q globular heads must bind to antibody before the complement cascade is triggered.

*#** C1r and C1s become activated when at least 2 C1q heads are antibopdy-bound.

#** C1r

*#*** Form the enzyme C1 esterase.  

#** C1s.  

*#* C1 esterace first digests C4 to C4a and C4b.  

#* C1r and C1s become activated when at least 2 C1q heads are antibopdy-bound.

*#** C4b binds to the antigen.

#** Form the enzyme C1 esterase.  

*#* C4b then binds C2.

# C1 esterase first digests C4 to C4a and C4b.  

*#** C2 is digested by C1 esterase to form C2a and C2bThe C4b2b complex is an enzyme (C ) that is capable of efficient digestion of C3 into C3a and C3b. The production of C3b can now be amplified by the same mechanism as the alternative pathway. The binding of one C1q molecule produces one C1 esterase molecule that then cause the binding of many hundreds of C molecules. The C3b molecule that is produced by the action of this enzyme can also bind to it, forming the complex enzyme C , which is the second enzyme capable of activating C5 and initiating the MAC. Like the alternative pathway, the major effects of classical pathway activation are to produce iC3b and hence it promotes phagocytosis and initiates inflammation.

#* C4b binds to the antigen.

# C4b then binds C2.

#* C2 is digested by C1 esterase to form C2a and C2bThe C4b2b complex is an enzyme (C ) that is capable of efficient digestion of C3 into C3a and C3b. The production of C3b can now be amplified by the same mechanism as the alternative pathway. The binding of one C1q molecule produces one C1 esterase molecule that then cause the binding of many hundreds of C molecules. The C3b molecule that is produced by the action of this enzyme can also bind to it, forming the complex enzyme C , which is the second enzyme capable of activating C5 and initiating the MAC. Like the alternative pathway, the major effects of classical pathway activation are to produce iC3b and hence it promotes phagocytosis and initiates inflammation.

. All the Ca fragments (C2a, C3a, C4a, C5a) are chemotactic for neutrophils and are potent inducers of acute inflammation (they are termed the anaphylotoxins).  

. All the Ca fragments (C2a, C3a, C4a, C5a) are chemotactic for neutrophils and are potent inducers of acute inflammation (they are termed the anaphylotoxins).  

*# '''The binding of soluble lectins to pathogens'''.  

*# '''The binding of soluble lectins to pathogens'''.