Complement System: Classical Pathway

Question 1

Initiation and significance of molecules involved

Answer 1

Blood plasma protein C1q detects antibodies on microbe by recognizing the Fc portion of the antibody

antibodies are produced by B cells, so the classical PW is an important arm of humoral (adaptive) immunity

innate system molecules in the pentraxin class can also bind to Fc and trigger the classical PW

both innate and adaptive

Question 2

The process of the classical pathway

Answer 2

C1q rec. Fc portion of antibody on microbe/antigen/antibody complex —>

C1r and C1s proteolytically cleave C4 and C2: C4b/C2a form C3 Convertase

C3 is cleaved into C3a and C3b

C3a goes on to be an inflammatory agent

C3b is a chemoattractant that binds to microbe and attracts other proteins to form C5 convertase

C5a causes vasodilation, C5B remains attached to microbe, combines with C6,7,8,9 = MAC attack complex

Question 3

C3 convertase is formed by

Answer 3

C4b/C2a

Question 4

C3 cleavage produces

Answer 4

pts a and b

Question 5

what parts of the C3 do what

Answer 5

pt-a is an inflammatory chemoattractant for neutrophils

pt-b binds to other complement proteins to form C5 convertase: C5 Convertase cleave C5, releasing pts a and b

Question 6

C5 cleavage produces

Answer 6

C5a and C5b

C5a potent chemoattractant, induces permeability of vessels

C5b reamins on microbe: attracts 6,7,8,9 to produce MAC

Question 7

MAC does what

Answer 7

causes lysis of cells where activated

Question 8

Classical complement system’s similarities to other pathways

Answer 8

similar to LECTIN pathway’s use of C4 and C2 initially, producing C3 convertase, and leading to the formation of MAC

all the steps are the same to LECTIN pw, except the ligand that triggers the formation of MAC