Practice #5 complement system

Question 1

How can C1qrs can be activated in the classical pathway of complement system?

Answer 1

By binding to at least 2 Fc regions of closely bound IgGs or by binding to IgM

Question 2

C3 can spontaneously be hydrolysed to C3a and C3b in the blood, what factors stabilize C3b when there is no need for it?
What stabilizes it on the surface of the microbe?

Answer 2

Factor I and H

Properdin

Question 3

If the inactive B factor binds to soluble C3b what inhibits them?

Answer 3

CR1, MCP, H factor

Question 4

Inhibitor of bound C4b

Answer 4

C4bp

Question 5

Inhibitors of bound C3b

Answer 5

DAF, MCP, CR1

Question 6

Inhibitor of C3a C5a

Answer 6

Serum carboxypeptidase N

Question 7

Inhibitors of MAC

Answer 7

CD59 (protectin)

Clustrin + Protein S

Question 8

Activation of the classical pathway

Answer 8

Ag-Ab immune complexes

Question 9

Activation of the alternative pathway

Answer 9

Spontaneous hydrolysis of C3 on oligosaccharide pathogenic surfaces

Question 10

Activation of the lectin pathway

Answer 10

PAMP recognition by MBL

Question 11

3 outcomes of complement activation

Answer 11

1. Lysis by MAC (C5b-C9)
2. Opsonization and phagocytosis (C3b)
3. Inflammation (C3a, C5a, CR)

Question 12

The role of complement system in B cell activation

Answer 12

Co binding of:
BCR- pathogen
CR2(CD21)- C3b on the pathogen
Result in enhanced BCR signaling

Question 13

CD21 is a marker for

Answer 13

B cells but not plasma cells

Question 14

Indications for complement detection tests

Answer 14

1. Family history of complement deficiency
2. Recurrent bacterial infections
3. Rheumatologic immunological diseases
4. Glomerulonephritis
5. Generalized edema with or without urticaria

Question 15

Complement functional tests

Answer 15

To detect the activity of complement factors or overall cascade

1. CH50/CH100 for the total activity of the classical pathway
2. AH50 for the total activity of the alternative pathway
3. Detection of particular complement particles (ELISA)
4. C1inh activity test (chromogen test)

Question 16

CH50 test

Answer 16

CH50 value: serum dilution that lyses 50% of the sheep RBCs

Sheep RBCs are covered by anti sheep Ab (Fc region exposed)
(sialic acid is present on the surface of RBCs, therefore not recognized by the alternative pathway)
Mix in the patient sera
Yes hemolysis: complement activity is good
No hemolysis: Problem in complement activity further examinations with ELISA

Question 17

AH50

Answer 17

Rabbit RBCs covered by anti sheep Ab (Fc region exposed)
Take out Ca2+ from the surface of the RBC and insert Mg2+ (without Ca2+ classical and lectin pathways wont occur)
Mix with the patient sera
Yes hemolysis: complement activity is good
No hemolysis: Problem in complement activity further examinations with ELISA

Question 18

CH50 value is affected by

Answer 18

1. Amount of complement proteins (rise or drop)

2. If some complement proteins are missing

Question 19

Liposome immunoassay

Answer 19

Mix liposome with G6PDH + anti liposome Ab
Mix the patient serum
6 phospho D glucono lactone is the substratefor G6PDH, if G6PDH will be released upon lipolysis we can detect NADPH product with a chromogen
Yes lipolysis: complement activity is good
No lipolysis: Problem in complement activity further examinations with ELISA

Question 20

Other immunoanalytical examinations for complement proteins (other then CH50, AH50 and liposome immunoassay)

Answer 20

1. IF
2. ELISA
3. Nephelometry
4. WB

Question 21

Dx if complement activation increases

Answer 21

1. Tumor
2. Infection
3. Ulcerative colitis

Question 22

Dx if complement activation decreases

Answer 22

1. Cirrhosis
2. Glomerulonephritis
3. HAE
4. Hepatitis
5. Kidney transplant rejection
6. SLE
7. Malnutrition

Question 23

HAE hereditary angioedema

Answer 23

C1inh deficiency
Since C1inh has a function also in the intrinsic pathway of the coagulation cascade 
1. inhibits XIIa
2. inhibits XIa
3. inhibits kallikrein 

without inhibition of kallikrein, pon the slightest infection there will be a massive froduction of BK causing vascular permeability to increase resulting in edema

Treatment is to give C1inh

Question 24

What complement proteins will be activated in HAE?

Answer 24

Only the upstream components:
Uninhibited C1 - C4b and C2b are produced at increased rate - without membrane to bind on C4b will be inactivated - therefore C4b and C2b are constanty consumed without forming C3 or C5 convertase
So no C3 or C5 activation

Question 25

PNH paroxysmal nocturnal hemoglobinuria

Answer 25

CD55/CD59 (protectin) is defected and there is no proper inhibition of MAC leding to erythrocytosis mainly at night when there is mild acidosis.
Hb from the lysed RBCs will exit in the urine

Question 26

Complement deficiencies

Answer 26

Primary (hereditary)

Secondary either by insufficient production or by constant consumption

Question 27

Complement as a tool - complement fixation test

Answer 27

Ag detection
Mix pt blood with Ab against its RBCs and the desired Ag
If the antigen is present complement proteins will bind to the Ab on the Ag and the RBCs will remain intact
No hemolysis- positive reaction

Ab detection
Mix pt serum with antigen and complement proteins
If there are Abs aginst the antigen they will bind to it
Mix sheep RBCs with anti sheep Ab
Complement proteins wont lyse the RBCs if they are already bound to the Ab
No hemolysis- positive reaction