Complement System

Question 1

How many plasma proteins__?

They circulate in an __________ form?

What is the crucial step in their activation?

Answer 1

20
inactive form

cleavage of C3 is the crucial step in their activation, and c3 is the most abundant complement protein

Question 2

What activates the classical pathway?

Answer 2

Binding of C1 complement to antibody IgM or IgG already bound to antigen

Question 3

What activates the alternative pathway?

Answer 3

triggered by microbial surface molecules (endotoxin, LPS), complex polysaccharides, cobra venom, and other substances in the absence of antibody…..

Question 4

What activates the lectin pathway?

Answer 4

triggered by plasma mannose binding protein linking to microbial carbohydrates

Question 5

all 3 pathways lead to formation of _________?

Answer 5

C3 convertase

C3 convertase splits C3 into C3a and C3b

Question 6

What does C3b do?

Answer 6

It remains bound to the microbe or cell where compliment is being activated

Here it starts the process of creating the MAC

C3b also acts as an opsonin. promotes phagocytosis by binding with its other arm to neutrophils and macropages.

Question 7

What does C3a do?

Answer 7

C3a gets released
It stimulates mast cells to release histamine
an anaphylotoxin

Question 8

What does C5a do?

Answer 8

• C5a gets released
• it’s an anaphylatoxin that stimulates mast cells to release histamine
• chemotactic for neutrophils, monocytes, eosinophils, and basophils
• also, activates the lipoxygenase pathway in neutrophils and monocytes……leukotrienes get produced and further promote inflammation

Question 9

Anaphylaxis

fainting, hoarseness, nausea, abd cramps

Answer 9

a syndrome of vasodilatory shock (low blood pressure)
edema
bronchoconstriction

Question 10

C6-C9 mainly help form MAC

MAC IS most important for defense against ____?

Answer 10

Group of bacteria, Neisseria

Question 11

Complement regulatory proteins?

Answer 11

C1 inhibitor

CD59

DAF

Question 12

C1 Inhibitor

Answer 12

block activation of classical pathway

A deficiency in this, hereditary angioedema

Question 13

DAF and CD59 have what in common?

They are associated with what deficiency?

Answer 13

-> both are linked to plasma membranes by a glycophosphatidyl (GPI) anchor

An aquired deficiency of the enzyme that creates GPI anchors…..paroxysmal nocturnal hemoglobinuria (PNH)

PNH: LACK DAF AND CD59, excessive complement activation, lysis of red cells

Question 14

DAF: Decay Accelerating Factor

Answer 14

• GPI anchor

- prevents formation of the C3 convertase

Question 15

CD59

Answer 15

• GPI anchor present

- inhibits formation of the membrance attack complex MAC