Practice #5 complement system Flashcards
How can C1qrs can be activated in the classical pathway of complement system?
By binding to at least 2 Fc regions of closely bound IgGs or by binding to IgM
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?
Factor I and H
Properdin
If the inactive B factor binds to soluble C3b what inhibits them?
CR1, MCP, H factor
Inhibitor of bound C4b
C4bp
Inhibitors of bound C3b
DAF, MCP, CR1
Inhibitor of C3a C5a
Serum carboxypeptidase N
Inhibitors of MAC
CD59 (protectin)
Clustrin + Protein S
Activation of the classical pathway
Ag-Ab immune complexes
Activation of the alternative pathway
Spontaneous hydrolysis of C3 on oligosaccharide pathogenic surfaces
Activation of the lectin pathway
PAMP recognition by MBL
3 outcomes of complement activation
- Lysis by MAC (C5b-C9)
- Opsonization and phagocytosis (C3b)
- Inflammation (C3a, C5a, CR)
The role of complement system in B cell activation
Co binding of:
BCR- pathogen
CR2(CD21)- C3b on the pathogen
Result in enhanced BCR signaling
CD21 is a marker for
B cells but not plasma cells
Indications for complement detection tests
- Family history of complement deficiency
- Recurrent bacterial infections
- Rheumatologic immunological diseases
- Glomerulonephritis
- Generalized edema with or without urticaria
Complement functional tests
To detect the activity of complement factors or overall cascade
- CH50/CH100 for the total activity of the classical pathway
- AH50 for the total activity of the alternative pathway
- Detection of particular complement particles (ELISA)
- C1inh activity test (chromogen test)
CH50 test
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
AH50
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
CH50 value is affected by
- Amount of complement proteins (rise or drop)
2. If some complement proteins are missing
Liposome immunoassay
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
Other immunoanalytical examinations for complement proteins (other then CH50, AH50 and liposome immunoassay)
- IF
- ELISA
- Nephelometry
- WB
Dx if complement activation increases
- Tumor
- Infection
- Ulcerative colitis
Dx if complement activation decreases
- Cirrhosis
- Glomerulonephritis
- HAE
- Hepatitis
- Kidney transplant rejection
- SLE
- Malnutrition
HAE hereditary angioedema
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
What complement proteins will be activated in HAE?
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
PNH paroxysmal nocturnal hemoglobinuria
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
Complement deficiencies
Primary (hereditary)
Secondary either by insufficient production or by constant consumption
Complement as a tool - complement fixation test
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
