Complement system and disorders|Immune response|Immunology|First Aid Lectures|Lec14 #drjamillectures
Channel: Dr. Jamil Lectures
Date: 31/03/2022

In this lecture we will discuss about Complement system,Its activation pathways;1.classic pathway 2.lectin,manose binding pathway 3.Alternative pathway.
its functions like opsinization,anaphylaxis,cytolysis and chemotactation and inhibitors.we will also discuss about its disorders

https://youtu.be/goy1jFGlqpk
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Complement
 System of hepatically synthesized plasma proteins that play a role in innate immunity and inflammation. Membrane attack complex (MAC) defends against gram ⊝ bacteria. The CH50 test is used to screen for activation of the classical complement pathway.
ACTIVATION PATH WAYS 
Classic—IgG or IgM mediated.
Alternative—microbe surface molecules.
Lectin—mannose or other sugars on microbe surface.
FUNCTIONS 
C3b—opsonization.
C3a, C4a, C5a—anaphylaxis.
C5a—neutrophil chemotaxis.
C5b-9 (MAC)—cytolysis.
Opsonins—C3b and IgG are the two 1° 
opsonins in bacterial defense; enhance 
phagocytosis. C3b also helps clear immune 
complexes.
Inhibitors—decay-accelerating factor (DAF, 
aka CD55) and C1 esterase inhibitor help 
prevent complement activation on self cells.
Complement disorders 
Complement protein deficiencies
Early complement deficiencies (C1-C4)
Increased risk of severe, recurrent pyogenic sinus and respiratory tract infections. Increased risk of SLE. 
Terminal complement deficiencies (C5–C9)
Increased susceptibility to recurrent Neisseria bacteremia.
Complement regulatory protein deficiencies
C1 esterase inhibitor deficiency
Causes hereditary angioedema due to unregulated activation of kallikrein increase bradykinin. 
Characterized by decrease C4 levels. ACE inhibitors are contraindicated (also increase bradykinin).
Paroxysmal nocturnal hemoglobinuria
A defect in the PIGA gene preventing the formation of glycosylphosphatidylinositol (GPI) anchors for complement inhibitors, such as decay-accelerating factor (DAF/CD55) and membrane inhibitor of
reactive lysis (MIRL/CD59). Causes complement-mediated intravascular hemolysis decreases haptoglobin, dark urine.


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