plasma protein composition and its function

1. PLASMA PROTEIN
COMPOSITION AND
ITS FUNCTION
Dipesh Tamrakar
M.Sc. Clinical Biochemistry
1

2. OVERVIEW
Introduction
Functions
Electrophoretic characteristics
Various plasma proteins
2

3. Plasma is a Straw colored liquid portion of blood
It is obtained as supernatant when anticoagulated
blood is centrifuged leaving the cell components
as precipitate.
55–60% of blood is made up of plasma.
consists of: water, electrolytes, metabolites,
nutrients, hormones, immunoglobulins and other
proteins.
Plasma proteins constitute approx. 4% of the
body’s total protein.
INTRODUCTION
3

4. Almost all plasma proteins, except
immunoglobulins are synthesized in liver
Plasma proteins are generally synthesized on
membrane-bound polyribosomes
Most plasma proteins are glycoproteins
In lab, separation of plasma proteins can be done
by salting out methods.
Fibrinogen is precipated by 10% and globulin by
22% of conc Sodium Sulfate
NH4SO4 precipitates globulins at half saturation
and albumin at full saturation.
INTRODUCTION
4

5. TOTAL PLASMA PROTEINS
•The normal serum total protein level is 60-80
g/L.
•The type of proteins in serum include:
a. Albumin (35-50 g/L)
b. Globulins (25-35 g/L)
α− globulin: α1 & α2−globulins
β− globulin: β1 & β2 globulins
γ− globulins
c. Fibrinogen (2-4 g/L)
A/G ratio: 1.2:1 - 1.5:1.
5

6. FUNCTIONS OF PLASMA
PROTEINS
1. Transport
2. Osmotic regulation
3. Catalytic function
4. Protective function
6

7. SPECIFIC FUNCTION OF
SOME PROTEIN
PROTEIN PLASMA CONC. FUNCTION
Pre-albumin 25 – 30 mg/dl Transport thyroxine to some
extend, Indicator of nutrition
Albumin 3.5 – 5.0 g/dl Transports fatty acids, bilirubin,
calcium, many drugs etc.,
colloid oncotic pressure
α1-globulin
α1-antitrypsins
0.3 – 0.5 g/dl
<0.2 g/dl combines with elastase, trypsin
and protects the hydrolytic
damage of tissues such as
lungs
Orosomucoid <0.1 g/dl Binds with progesterone
Retinol binding
protein (RBP)
3 – 6 mg/dl Transport Vit A
Thyroxine
binding globulin
1 – 2 mg/dl Transports thyroid hormones
7

8. PROTEIN PLASMA CONC. FUNCTION
Transcortin or
Cortisol binding
protein (CBG)
3 – 4 mg/dl Major transporter of
steroid hormones (eg;
cortisol, corticosterone)
α2-globulins
a) Ceruloplasmin
b) Haptoglobulin
0.4 – 0.8 g/dl
0.15 – 0.60 g/l
<0.3 g/dl
-Copper transport
-Binds with plasma free
haemoglobin
α2-macroglobulin 0.2 – 0.3 g/dl Transports antitrypsin and
antiplasmin activity
Prothrombin <0.02 g/dl Participate in blood
coagulation
Fibrinogen 0.2 – 0.4 g/dl Participate in blood
coagulation
CRP 0.01 g/l Acute phase reactant:
motivates phagocytosis in
inflammatory disease
8

9. PROTEIN PLASMA CONC. FUNCTION
β-Globulins
a. Transferrin
b. Hemopexin
c. Plasminogen
d. -
Lipoproteins
0.6 – 1.1 g/dl
0.2 – 0.3 g/dl
<0.1 g/dl
<0.05 g/dl
0.2 – 0.5 g/dl
transport Iron
transport Haem
involves in Fibrinolysis
transport Triglycerides and
cholesterol
γ-Globulin
a. Ig A
b. Ig M
c. Ig G
d. Ig E
e. Ig D.
0.8 – 1.8 g/dl
150 – 400 mg/dl
50 – 200 mg/dL
800-1500 mg/dL
0.02 – 0.05 mg/dl
1 – 10 mg/dl
Antibody functions
protects the body surface
humoral immunity, serves
as first line of defense
mostly humoral immunity
humoral sensitivity &
histamine release
B-cell receptor
C4
complement
C3
complement
0.20 – 0.65 g/l
0.55 –1.80 g/l
0.15 g/l
Immune response
Immune response
Immune response
9

10. Electrophoresis
Migration of the charged molecules in an electric
field.
Negative charged particles (anions) move towards
anode and positively charged particles (cations)
move towards cathode.
Proteins contain charges due to the presence of
amino group (NH3+) and carbonyl group (COO-)
All major serum proteins carry a net negative charge
at pH 8.6 and migrate toward the anode.
In agar gel electrophoresis, normal serum is
separated into 5 bands.
1) Albumin : 55 - 65%
2) Alpha-1-globulin : 2 - 4%
3) Alpha-2-globulin : 6 -12%
4) Beta-globulin : 8 -12% 10

11. Electrophoresis
Albumin has the maximum mobility (obvious
band) and gamma globulin has the minimum
mobility.
α-1-globulins consist almost entirely of α1-
antitrypsin and
α1-antichymotrypsin.
α2-globulins consist mainly of α 2-
macroglobulin and haptoglobin.
β-globulins often separate into two; β1;
transferrin with a contribution from low density
lipoprotein (LDL), and β2; C3 component of
complement.
γ-globulins are immunoglobulins; some11

12. Electrophoresis
The width of the band depends on the number of
proteins present in that fraction.
Homogeneous protein gives a narrow band.
stained with dyes such as Ponceau S or Amido
black or Coomassie blue.
cleared transparent medium scanned in
densitometer
light is transmitted through it to a phototube to
record the absorbance of the dye that is bound to
each protein fraction.
absorbance is recorded on a strip-chart recorder
12

13. 13

14. 14

15. ABNORMAL PATTERNS IN CLINICAL
DISEASES
Chronic infections gamma globulins are
increased (smooth and
widebased)
Multiple myeloma sharp spike of M-band noted
between beta and gamma
Fibrinogen
(If plasma is used)
prominent band in the gamma
region, which may be
confused with the M-band
Primary immune deficiency Gamma globulin fraction is
reduced
Nephrotic syndrome alpha-2 fraction (containing
macroglobulin) will be very
prominent.
Cirrhosis of liver there are some fast-moving
gamma-globulins that
prevent resolution of the β-
and gamma-globulin bands.
15

16. ABNORMAL PATTERNS IN CLINICAL
DISEASES
Inflammatory condition Decrease in albumin, and
increase in acute phase
reactants like α1-globulins
(α1-acid glycoprotein, α1-
antitrypsin), α2-globulins
(ceruloplasmin and
haptoglobin), and β-globulin
band (C-reactive protein)
Chronic lymphatic leukemia gamma globulin fraction is
reduced
Alpha-1-antitrypsin
deficiency
alpha-1 band is thin or even
missing
16

17. PREALBUMIN
(TRANSTHYRETIN)migrates ahead of albumin in the
electrophoresis of serum
Molecular weight 55000 Dalton
transport protein for thyroxine and
triiodothyronine
it also binds with retinol-binding protein that
transports retinol (vitamin A) and is rich in
tryptophan
Decrease
hepatic damage
acute-phase
inflammatory
response
tissue necrosis
malignancy
Increase
patients receiving
steroids
alcoholics,
in chronic renal
failure
17

18. ALBUMIN
name is derived from the white precipitate formed
when egg is boiled (Latin, albus = white).
M.W: 69,000 D.
Consists of single polypeptide chain of 585 a.a. with
17 disulfide bonds & High net negative charge at
physiological pH.
Constitutes  60% of the total plasma protein; most
abundant plasma protein.
Half-life: 20 days.
Secondary structure
 >50% is in the α-helical conformation.
 15% as β-pleated structure
 and remaining in random coil conformation.
The tertiary structure - globular protein. 18

19. Synthesis
by the liver. (exception- early fetal life; by yolksac)
synthesis- 12 g/day
Synthetic rate controlled by
 Colloidal Osmotic Pressure (primarily)
 protein intake ( secondarily)
inflammatory cytokines decrease synthesis
release decreases by hypokalemia.
Catabolism
by pinocytosis by all tissue  lysosomal catabolism
Small amounts ( 10-20%) lost in GIT and the
glomerular filtrate.
Distribution
2 Compartments: intravascular (40%) & extravascular
(60%). 19

20. Albumin leaves the circulation at a rate of 4%–5% of
total intravascular albumin per hour - transcapillary
escape rate (TER)
Albumin is responsible for nearly 80% of the colloid
osmotic pressure of the intravascular fluid,
It maintains the appropriate fluid balance in the
tissue.
Transport: (4 binding sites on albumin):
bilirubin, free fatty acid, Phospholipids, cholesterol,
amino acid
steroid hormones, thyroine
drugs (sulfonamides, aspirin, salicylate, phenytoin)
 metal ions Ca2+ , Cu2+
Buffering action: Albumin has a total of 16 histidine
residue that conributes to its buffering action.
Nutritional function : serves as a source of amino20

21. CLINICAL SIGNIFICANCE
Decrease conditions:
malnutrition and malabsorption
Liver disease, resulting in decreased
synthesis
Protein-losing enteropathy
Renal failure
burns or exfoliative dermatitis
Hypothyroidism
Acute disease states
Mutation resulting from an autosomal
recessive trait causing analbuminemia
or bisalbuminemia
Redistribution by hemodilution,
Increased
condition :
Seldom; clinically
important
 with
dehydration or
 after excessive
albumin
infusion.
21

22. CLINICAL APPLICATIONS
Albumin–fatty acid complex cannot cross BBB and
hence fatty acids cannot be taken up by brain.
Calcium level in blood is lowered in
hypoalbuminemia. Calcium is lowered by 0.8 mg/dl
for a fall of 1 g/dl of Albumin.
Human albumin is therapeutically useful to treat
burns, hemorrhage and shock.
Hypo-albuminemia will result in tissue edema
(Starling's law).
In micro-albuminuria or pauci-albuminuria, small22

23. GLOBULINS
M.W.: 90,000 to 13,00,000
Site of synthesis
α-and β-globulins are synthesized in the liver.
But γ-globulins are synthesised by plasma cells.
α-Globulins
are glycoproteins
classified into α1 and α2 depending on their
electrophoretic mobility
23

24. 1. α1-acid glycoprotein
Also called as orosomucoid
Is negatively charged even in acid solutions
183 amino acids; 40 kDa; 45% is carbohydrate,
including about 12% sialic acid
produced by the liver
half -life of about 3 days
is an acute-phase reactant
Normally present in 0.6 - 1.4 g/l
Functions:
transport protein for progesterone and basic drugs
carry needed carbohydrate constituents to the sites
of tissue repair following injury.
24

25. CLINICAL IMPORTANCE
Increase
in acute and chronic
inflammatory diseases
cirrhosis of the liver
malignant conditions
stress,
acute myocardial
infarction, trauma,
pregnancy,
pneumonia,
rheumatoid arthritis,
and surgery.
Decrease
In generalised
hypoproteinaemic
conditions,
hepatic diseases
malnutrition
nephrotic syndrome.
25

26. 2. α1-Antichymotrypsin
a member of the serine proteinase inhibitor
(serpin) family.
Inhibits cathepsin G, pancreatic elastase, mast cell
chymase, and chymotrypsin.
produced in the liver.
is an acute-phase protein.
Decreased in liver disease.
Associated with Alzheimer disease as it is an
integral component of the amyloid deposits in
Alzheimer disease
26

27. 3. GC - GLOBULIN (GROUP-SPECIFIC
COMPONENT; VITAMIN D–BINDING
PROTEIN)
27
major carrier protein of vitamin D and its metabolites
in the circulation (importance for bone formation
and immune system) also transports fatty acids and
endotoxin
Gc may act as a co-chemotactic factor in facilitating
chemotaxis of neutrophils and monocytes in
inflammation.
Increase
third trimester of pregnancy
Patients taking estrogen therapy
oral contraceptives
Decrease

28. 4. α1-fetoglobulin (AFP)
present in high concentrations in fetal blood during
mid-pregnancy
decrease gradually after birth, reaching adult levels
by 8–12 months.
In normal fetuses, AFP binds the hormone estradiol.
Normal adult blood level : <1 μg/dl.
May increase during pregnancy
Marker of hepatocellular carcinoma or
teratoblastomas
elevated AFP level :- spina bifida, neural tube
defects, abdominal wall defects, anencephaly
Low levels of maternal AFP:- increased risk for Down
syndrome and trisomy 18, neural tube defects.
28

29. 5. α1-antitrypsin (α1-AT)
Synthesized by hepatic parenchymal cells.
principal protease inhibitor (Serpin family) of human
plasma
inhibits trypsin, elastase
M.W.: 45,000 to 54,000
Normal value in adults: 2 to 4 g/L
Physiologically, it is the most important inhibitor of
leukocyte elastase released during phagocytosis by
leucocytes (protective role)
if deficiency of AAT is present, unchecked action of
the leukocyte elastase cleaves elastin, which is
important for maintaining the architecture o lung
tissue.
Loss of elastin leads to emphysema. 29

30. Α1-ANTITRYPSIN DEFICIENCY HAS BEEN
IMPLICATED IN 2 DISEASES: EMPHYSEMA AND
Α1-ANTITRYPSIN DEFICIENCY LIVER DISEASE
Increase
one of the acute phase
reactant (APR), so
increased in trauma,
burns, infarction,
malignancy, liver
disease, etc.
Pregnancy
contraceptive
medication
Decrease
In protein losing
disorders, e.g.
nephrotic syndrome
diffuse
hypoproteinaemias
juvenile cirrhosis of
liver
Respiratory diseases
emphysema
30

31. Emphysema: (emphusanG=to inflate)
Abnormal distension of lungs by air
Associated with lung infections and increase in activity
of macrophages to release elastase that damage lung
tissues
In the normal circumstances, elastase activity is
inhibited by α1-antitrypsin
Effect of smoking on α1-antitrypsin:
the a.a methionine at position 358 is involved in
binding with protease
Smoking causes oxidation of this methionine to
methionine sulfoxide
As result α1-antitrypsin with methionine sulfoxide
cannot bind and inactivate proteases
31

32. 32
α1-antitrypsin deficiency liver disease:
Due to accumulation of mutant α1-antitrypsin which
aggregates to form polymers
Aggregation is due to formation of loop-sheet
polymerization
hepatocytes cannot secrete these polymers.
These polymers in turn cause liver damage
(unknown mechanism) followed by cirrhosis
Role as a tumour-marker
α1-AT increased in germ cell tumours of testes and
ovary
As an Inhibitor of Fibrinolysis
α1-AT is one of the most important inhibitors to
fibrinolysis along with α2-antiplasmin and α2-

33. Α2-GLOBULINS
1.Alpha-2-Macroglobulin (AMG)
major component of alpha-2 globulins
large plasma glycoprotein (M.W.: 720 kD).
tetrameric protein (made up of four identical subunits
of 180 KD).
Synthesized by hepatocytes and macrophages
Normal serum level is 130-300 mg/dl
33

34. Functions of AMG
inactivates all proteases
Act as an important in vivo anti-coagulant
AMG is the carrier of many growth factors such as
platelet derived growth factor (PDGF)
Approx. 10 % of the zinc in plasma is transported by
α2-macroglobulin and the remainder being
transported by albumin
Clinical Importance
AMG is markedly increased (up to 2-3 g/dl) in
Nephrotic syndrome, where other proteins are lost
through urine.
34

35. Ceruloplasmin
copper containing α2-globulin (Glycoprotein)
Single polypeptide chain; 1046 AAs
with 3 glycosamine linked
oligosachharide side chains.
blue in color (Latin, caeruleus= blue).
M.W: ≈151,000
Synthesis: mainly by liver where 8 copper atoms are
attached to apocaeruloplasmin.
& small portion by lymphocytes and macrophages
normal plasma half-life is 4-5 days.
35

36. Functions of Ceruloplasmin
It has enzyme activities of copper oxidase,
histaminase and ferrous oxidase.
mainly functions as a ferroxidase
i.e. helps in oxidation of Fe++ to Fe+++ which can be
incorporated into transferrin.
90 % or more of total serum copper is contained in
ceruloplasmin and 10% is bound to albumin.
carries 0.35 % Cu by weight
has eight sites for binding copper [½ as cuprous
(Cu+) and ½ as cupric (Cu++)]
Copper is bound with albumin loosely, and so easily
exchanged with tissues. Hence transport protein for
copper is Albumin.
Normal conc of serum ceruloplasmin is 25 – 50
mg/dl 36

37. Clinical Importance
Increase
pregnancy, inflammatory processes, malignancies,
oral oestrogen therapy and contraceptive pills.
37
Decrease
Wilson’s disease and Menke’s disease.
malnutrition, nephrosis, and cirrhosis

38. Wilson's Disease
inherited autosomal recessive condition.
defect is a mutation in a gene encoding a copper
binding ATPase which links copper to
ceruloplasmin and releases it into the bloodstream
Clinical features:
Accumulation of copper in liver leads to hepatocellular
degeneration and cirrhosis.
Deposit in brain basal ganglia leads to lenticular
degeneration and neurological symptoms.
Cu deposition in kidney causes renal damage
resulting excretion of amino acids, glucose, peptides
and Hb in urine
Copper deposits seen as green or golden pigmented
ring around cornea; this is called Kayser–Fleischer38

39. Menkes disease
Also called “kinky” or “steely” hair disease.
It is X-linked disease, so affects only male infants
and is usually fatal in infancy.
Cause: mutations in the gene for a copper-binding
P-type ATPase.
intestinal copper uptake by brush border cells is
normal, but copper transport to other tissues is
affected.
This causes reduced activity of numerous copper
containing enzymes necessary for structure and
function of bone, skin, hair, blood vessels, etc.
39

40. Haptoglobin
composed of two kinds of polypeptide chains, two
α-chains (possibly three) and only one form of β-
chain.
These 4 pp chains linked by disulfide bonds. 90,000
dalton
Synthesised mainly in liver, very small extent by RE
cells
Phenotypes: In Human; 3 polymorphic forms Hp1-1,
Hp 2-1 and Hp2-2.
Functions of Haptoglobin
binds free Hb by its α-chain
and minimises urinary loss of Hb
(Abnormal Hb such as Bart’s-Hb and Hb-H have no
α-chains and hence cannot be bound).
Hp-Hb complex (155000) cannot pass through
glomerular filter  destroyed by RE cells. 40

41. 41

42. CLINICAL IMPORTANCE
normal plasma levels for adults : 0.3-2.0
g/l
Increased plasma
levels
increased in
inflammatory
conditions.
Protein losing
syndromes –
compensatory
increase
DM, Duchenne-type
Muscular dystrophy,
melanoma
Decreased plasma levels
Hemolytic disease
[Hp levels sensitive
marker of in-vivo
hemolysis (in mismatched
blood transfusion reactions
and in HDN)].
Estrogens- decrease in
late pregnancy.
Newborn period – due to
hepatic immaturity 42

43. Β-GLOBULINS
Transferrin
non-heme iron-containing protein
Formerly called siderophilin
Glycoprotein
M.W. : 70,000
Protein part is apotransferrin which can bind two
atoms of Fe to form transferrin
normal plasma conc. is 1.8 to 2.7 g/l
has capacity to bind 3.4 mg of Fe per litre.
Normally transferrin is about 33 % saturated with Fe.
43

44. Site of synthesis
Principally by liver.
There is also evidence of its synthesis by bone
marrow, spleen, lymph nodes and lymphocytes.
Functions of Transferrin
transport of Fe between intestine and site of synthesis
of Hb and other Fe containing proteins.
unsaturated transferrin has a bacteriostatic function
which is attributed to sequestration of Fe required by
microorganisms.
44

45. CLINICAL IMPORTANCE OF
TRANFERRIN
Increase
In iron deficiency
anaemia
in last months of
pregnancy
estrogen
administration
Decrease
In protein calorie
malnutrition (PCM),
inflammation (negative
APR),
cirrhosis of the liver,
nephrotic syndrome,
acute illness such as
trauma,
myocardial infarction
and malignancies.
45

46. C-reactive Protein
Conc.: <1 mg/dl in the adult male
It precipitates with group C polysaccharide of
pneumococci, in the presence of Ca++, hence it is
named as “C-reactive protein”.
Two electrophoretic forms appear on
immunoelectrophoresis:
• CRP alone in the γ-band,
• a CRP complex with an acidic
mucopolysaccharide
termed m-CRP in the β-region.
46

47. Clinical Significance
It can bind to T-lymphocytes, LDL and can activate
complement.
Can act as an ‘opsonin’ in augmenting immunity
indicator of the early phase of an inflammatory
process. (Acute phase protein)
Plasma levels rises upto 2000 folds after MI, stress,
trauma, infection, inflammation, neoplastic
proliferation.
Plasma levels generally proportional to the degree of
tissue damage.
Increased hsCRP concn  +ve corelation in
predicting the risk of future coronary disease.
47

48. hsCRP
Immunologic methods; Nephelometry and EIA
measure CRP with sensitivity of approx. 3 – 5 mg/L
Recently developed monoclonal antibody-base CRP
methods can detect CRP levels below 1.0 mg/L
High sensitive or ultra sensitive CRP measured at low
levels (1 -10 ng/dl)
Marker for risk for atherosclerosis
1. <1.0 mg/L : Low risk
2. 1 – 3 mg/L : Moderate risk
3. >3 mg/L : High risk
4. >10.0 mg/L : Acute phase reaction
48

49. Haemopexin
M.W.: 57,000 to 80,000
Normal value in adults = 0.5 to 1.0 g/l
synthesized by parenchymal cells of liver.
Functions to bind and remove circulating haem
which is formed in the body from breakdown of Hb,
myoglobin or catalase.
It binds heme in 1: 1 ratio.
The haemhaemopexin complex is removed by the
parenchymal cells of liver.
49

50. CLINICAL SIGNIFICANCE OF
HAEMOPEXIN
Decrease
In haemolytic
disorders
At birth in newborns
Administration of
diphenylhydantoin
Increase
Pregnant mothers have
increased serum levels,
In diabetes mellitus
muscular dystrophy
Some malignancies,
especially melanomas.
50

51. Complement C1q
Complement is a collective term for several plasma
proteins that are precursors for certain active
proteins circulating in blood.
After the formation of immune complexes, C1q is the
first complement factor that is bound.
The binding takes place at the ‘Fc’ or constant part of
the IgG or IgM molecule.
The binding triggers the classical complement
pathway.
Properties
It is thermolabile and is destroyed by heating at 56°C
× ½ hour
51

52. The complement system helps the body
immunity in 4 ways:
1. Complement fixation:
 Binds to the foreign invading cells and causes
lysis of the cell membrane
2. Opsonization:
 Promotes the phagocytosis of foreign cells
3. Inflammatory reaction:
 Stimulates local inflammatory reaction and
attracts phagocytic cells
4. Clearance of Ag-Ab complexes:
 Promotes the clearance of Ag-Ab complexes
52

53. CLINICAL SIGNIFICANCE OF
COMPLEMENT C1Q
Increase
Certain chronic
infections
In rheumatoid arthritis
Decrease
In active immune
disease such as SLE
In protein synthesis
disorders
Protein losing
enteropathy
53
β-Lipoproteins (LDL)
Involved in the transport of cholesterol from liver to
extrahepatic tissue.
Increased: Nephrosis, Hyperlipidemias
Decreased: Starvation

54. ACUTE PHASE PROTEINS (OR
REACTANTS)
Positive APR
• C-reactive protein
(CRP)
• Haptoglobin (Hp)
• Ceruloplasmin
• α1-antitrypsin
• α1-acid glycoprotein
(orosomucoid) and
• fibrinogen
Negative APR
Some proteins in
inflammatory states
decrease;
those are called
negative acute phase
proteins.
Eg: Albumin
Transthyretin (pre-
albumin)
Transferrin
Retinol binding
protein 54

55. Fibrinogen
A soluble glycoprotein
also called as clotting factor I
synthesized in the liver
constitutes 4 to 6 % of total proteins of blood
Conc. In plasma is 200–400 mg/dL
M.W.: 3,50,000 and 4,50,000.
Functions as: the precursor to fibrin
form bridges between platelets by binding GpIIb/IIIa
surface membrane proteins.
55

56. Structure
large asymmetrical molecule,
highly elongated
made up of 6 polypeptide chains (hexamer): 2Aα, 2Bβ
and 2γ-chains thus formula is Aα2Bβ2 γ2.
Chains are linked together lengthwise by S-S linkages
Being asymmetrical and large, it is important for
viscosity of blood.
56

57. On the α and β chains of fibrinogen, there is a
small peptide sequence : fibrinopeptide (prevents
spontaneously forming polymers with itself)
the amino terminal ends of the chains, bear excess
of negative charge due to presence of aspartic acids
and glutamic acids residues.
negative charges  contribute to solubility of
fibrinogen in plasma.
Clinical significance
Congenital fibrinogen deficiency (afibrinogenemia)
Hypofibrinogenemia in DIC.
57

58. OTHER PLASMA PROTEINS
* Myoglobin:
Heme protein found in striated skeletal and cardiac
muscles
2% of total muscle protein with Mol wt 17,800 dal
(153 a.a)
Serum baseline varies with physical activity and
muscle mass (30 – 90 ng/ml in adults)
In AMI- increase seen within 1 – 3 hrs of onset and
reaches peak in 5 – 12 hrs and returns to normal in 18
– 30 hrs
58
* Troponin:
Complex of 3 proteins that bind to the thin filaments
of striated muscle (not in smooth muscle)
3 complex: troponin T (TnT), troponin I (TnI) &
troponin c (TnC)
Regulates muscle contraction
In AMI- increase seen within 3 – 6 hrs of onset and

59. OTHER PLASMA PROTEINS
* Fibronectin:
Glycoprotein with activities in cellular interactions
including roles in cell adhesion, tissue differentiation,
growth and wound healing.
Synthesized by the liver hepatocytes, endothelial cells,
peritoneal macrophages and fibroblasts
Fetal fibronectin is normally present in amniotic fluid
and placental tissue
Positive test >50 ng/ml indicates a high risk for
premature delivery
59

60. CLASSIFICATION
5 main classes
 (according to M.W and electrophoretic mobility)
60

61. 61
Fig: Diagram of human immunoglobulin G
(IgG)

62. Ig G (γG)
Major immunoglobulin making 75% of total Ig
65% of total Ig G is in plasma with 2 heavy chain and 2
light chain with mol wt 150 KDa.
4 subclasses: IgG1, IgG2, IgG3 & IgG4 (differ in hinge
region)
IgG1 is the principle IgG to cross placenta and protect
neonates for the first 3 mths of postnatal life
IgD (γD)
main function and the role is not yet determined
But, IgD along with IgM is the predominant Ig on the
surface of human B Lymphocytes
it has been suggested that IgD may be involved in the
differentiation of B lymphocytes.
62

63. IgM (γ M)
3rd most common serum Ig.
First Ig to produce in response to antigen
First Ig produced by neonate
Monomeric IgM  membrane bound antibody
in plasma  Pentameric IgM
IgM (with IgD) is the major Ig expressed on
the surface of B cells
Polymerisation
IgM exists as pentamer with M.W. approx.
900,000
there is a single J-chain in each IgM
pentamer. 63

64. IgA (γA)
2nd most common serum Ig.
Can be monomer, dimer, trimer or
tetramer
2 subclasses:
 IgA1 : mostly found in serum; made by
bone marrow B cells
 IgA2 : mostly found in secretions; made
by B cells located in the mucosae
Secretory IgA –dimer or tetramer
J-chain
Secretory component
The daily production of IgA is greater
than any other immunoglobulin class.
64

65. IgA is found in external secretions such as colostrum,
saliva, tears, GI fluids, prostatic secretion, vaginal
secretions, mucous secretions of small intestine,
nasal and bronchial secretions.
IgA inhibits bacterial colonisation and viral infection
of mucosal surfaces.
Secretory IgA is slightly different from serum IgA
 due to presence of another small protein, called as
transport piece (T-Protein or secretory protein or
transport protein).
65

66. IgE (γE)
Mediates immediate
hypersensitivity reaction
involved in allergic diseases
like hay fever, asthma, etc.
bind allergens and triggers the
release from mast cell allergic
mediators like histamine which
is responsible for the
characteristic wheal and flare
skin reactions
IgE defends against worm
infections (helminthes) by
causing release of enzymes
from eosinophils.
66

67. PARAPROTEINS
are immunoglobulins produced by a single clone of B
cells.
on electrophoresisdiscrete band, usually in the γ-
region.
Plasma electrophoresis  fibrinogen band may mask
a paraprotein.
Paraproteins (usually IgG or IgA)  most frequently
seen in multiple myeloma, solitary plasmacytoma,
and in Waldenström’s macroglobulinaemia (IgM).
Bence Jones protein in urine are present in about 75%
cases of myeloma.
In plasma, these Ig light chains of BJP are rapidly
cleared.
67

68. Clinical implication of Ig classes
68
Ig class Increase Decrease
Ig G Infections of all types
Hyperimmunization
Liver diseases, Severe
malnutrition
Rheumatoid arthritis
Agammaglobulinemia
Lymphoid aplasia, CLL
Bence Jones proteinemia
IgA myeloma
Ig M Waldenström's
macroglobulinemia
Malaria, Infectious
mononucleosis
Lupus erythematosus
Rheumatoid arthritis
Agammaglobulinemia
Lymphoid aplasia
CLL
Ig G and IgA myeloma
Ig A Cirrhosis of the liver (most
cases)
IgA myeloma
Agammaglobulinemia
Lymphoid aplasia, IgG
myeloma, ALL, CLL
Ig D Chronic infections, Ig D
myeloma, liver disease
-
Ig E Hay fever, Asthma Agammaglobulinemia

69. 69