Page 58 - Concise Pathology for Exam Preparation ( PDFDrive )

2 Acute and Chronic Inflammation 43

sites of infection or injury, however, to trigger a series of potent inflammatory events.
Their action occurs via three pathways:
1. Classical pathway (Flowchart 2.7)

Antigen–antibody (IgG or IgM) complex

Activation of the C1-complex (which consists of
one molecule C1q and two molecules C1r and C1s)

C1-complex binds to and splits C4 and then C2

R e s a e l e f o C b 4 n a d C a 2 DAF (bound to the erythrocyte
m e m e n a r b a i v a G h c n a I P ) r o

C4b and C2a bind to form the classical pathway C3-convertase (C4b2a complex)

Breakdown of C3 convertase
C3-convertase leads to cleavage of C3 into C3a and C3b

C3b joins with C2a and C4b (the C3 convertase) to
make C5 convertase
FLOWCHART 2.7. Classical pathway of complement activation.

2. Alternative pathway (Flowchart 2.8)

Factor B, Factor D

Direct hydrolysis of C3 C3b C3bBb C3Bb3b
e v i t a n r e t l a ( (alternative
h t a p w y a pathway
• Microbial C3 convertase, C5 convertase)
e c a f r u s stabilized by
P • - y l o Properdin)
saccharides
C5 convertase Cleaves C5 into

C5a and C5b
C5b complexes with
C6, C7, C8 and C9
Formation of
C5b6789
(membrane attack
complex or MAC)

Inserted into the cell membrane,
‘punches a hole’ and initiates cells lysis
FLOWCHART 2.8. Alternative pathway of complement activation.

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