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1. Globulins produced in response to antigenic stimulation
2. React specifically with Ag which stimulated their production
3. All antibodies are Igs, But all Ig (Myeloma proteins) are not antibodies

4. Structure- Y shaped, 4 polypeptide chain molecule 2 heavy, 2 light chains, held together by Disulphide bonds

5. Heavy chains α ,δ, ε, γ, μ    (A,D, E, G, M)

6. Light chains two types: k (Kappa)/ λ  (lamda); 2:1

7. Papain digestion: 2Fab (fraction antibody binding) + 1Fc

8. Fc (Fraction crystallisable)- function: Complement fixation, Binds to cell receptors (FcRs), Passage across placental barrier, Distinguish b/w different classes

9. Pepsin digestion: F(ab)2  +  Fc’

  IgG IgA IgM IgD IgE
Molecular Wt. (KDa) 150 160, 325* 900 180 190
 Sedimentation 7 7, 11* 19 7 8
Carbohydrate Content % 3 8 12 13 12
Heavy chain class γ 1,2,3,4 α1,2 μ δ ε
Light chain κ/λ κ/λ κ/λ κ/λ κ/λ
Serum conc. (mg/ml) 12 2 1.2 0.03 0.00004
Half life (days0 21 6 5 3 2
Complement binding Classical Alternate Classical None None
Binding tissue Heterologus None None None Homologus
Secretion from serous membranes No Yes* No No Yes
Placental passage Yes No No No No
Heat stability 56C Yes Yes Yes Yes No

Special points

  1. Secretory Ig A.
    1. VL and VH: Specific antigen binding site
    2. Isotypic determinants
      i. Distinguish H chain classes (Ig G,A,M,D,E) and subclasses (Ig G1,G2 etc) and κ and λ light chains
    3. Allotypic determinants
      i. Distinct amino acid residues located primarily in γ and α H chains and κ,λchains
      ii. Possessed by some individuals of a particular species
      iii. Reflect genetic polymorphism of Igs.
    4. Idiotypic determinants

                  i.    Located on V regions of L and H chains        


2.  Antigen antibody reactions

Antigen & antibody combine specifically

Non-covatent interaction- hydrophobic, Van der waals,  electrostatic and hydrogen bonds


B. Precipitation

  1. Antigen-soluble
  2. Sensitive for detection of antigen
    1. Ring test
    2. Slide test
    3. Tube test
    4. Immunodiffusion (precipitation in gel )
      1. Single diffusion in one dimension (Oudin’s method )
      2. Double diffusion in one dimension (Oaklevfulthorpe,s method)
      3. Single diffusion in two dimensions (Radial immunodiffusion)
      4. Double diffusion in two dimensions (Ouchterlony’s procedure)
      5. Immunoelectrophoresis
      6. Electroimmunodiffusion
  • CIEP
  • Rocket electrophoresis

C.  Agglutination

1.  Particulate antigen

  1. Slide Agglutination - For typing of Pneumococci, Streptococci, Salmonella & Shigella
  2. Tube Agglutination -For diagnosis of typhoid, brucellosis and Typhus fever
  3. Coomb's Test (Antiglobulin `Test) -Done to detect the presence of incomplete or blocking antibodies. Such antibodies combine with the antigen but do not result in agglutination e.g. Rh antibody. Blocking antibodies can also be detected by doing the test in hypertonic (5%) saline or albumin saline. Coomb's test is of 2 types -
    i.    Direct Coomb's Test - To detect the presence of Rh antibodies on the foetal RBCs present due to prior contact with maternal serum.
    Washed foetal RBCs are mixed with antihuman antibody. If agglutination takes place means coomb's test is positive and hence foetal RBCs contain maternal Rh antibody on their surface.
    ii.    Indirect Coomb's Test : This test detects presence of Rh antibody in maternal blood.
    Mother's serum is mixed and incubated with 0 +ve RBCs. RBCs are washed and then add antihuman immunoglobulin.
    Agglutination occurs, test is positive. Coomb's test also detects non agglutinating antibodies in Brucellosis.
  4. Passive / Indirect Agglutination :
    Here precipitation reaction is converted into agglutination by coating soluble Ag on the surface of a cell or particle e.g. Latex agglutination - For RA factor, CRP or ASO detection.
    Passive Hemagglutination - Ag coated on RBCs e.g. TPHA for syphilis
    Gelatin Agglutination - For HIV
    Reversed Passive Agglutination - When instead of Ag, Ab is coated on cell surface and test detects presence of Ag.
  5. Coagglutination:

Cowan strain I of Staph. aureus possesses protein A on its surface. Protein A can bind Fe portion of IgG molecules non specifically leaving Fab portion free of react with Ag. Thus Staph. aureus is combined with particular Ab and when homologous Ag is added to bacterial suspension, agglutination takes place. Used for-detection of bacterial antigens in serum, urine and CSF. Eg., Pneumo or Meningo or H. Influenza Ag in CSF of patients with Meningitis.


D. Complement Fixation Test

Other tests utilizing complement

  1. Immune adherence (V. cholerae, T. pallidum ) (C3b)
  2. Treponema pallidum immobilization Test
  3. Cytolytic / cytocidal test (V. cholera)

E.  Neutralization Tests

  1. Virus neutralization                 
  2. Toxin neutralization           
  3. Antistreptolysin O test (ASLO) (In-vitro)
  4. Nagler reaction (In-vitro)         
  5. Shick test (In-vivo)            
  6. Dick test (In-vivo)

F.  Immunofluorescence

  1. Direct immunofluorescence: for antigen detection (e.g. Rabies, Pneumocystis jerovici, pertussis, syphilis)     
  2. Indirect immunofluorescence: For antibody detection (FTA- ABS)


  1. Indirect           
  2. Competitive         
  3. Direct sandwich           
  4. Indirect sandwich
H. The Complement System
  1. Bacteriolysis/ Cytolysis
  2. Amplification of inflammatory response (c3a, c5a, Mal)
  3. Hypersensitivity reaction (type II, III)
  4. Endotoxic shock
  5. Immune adherence
  6. Opsonization (c3b)
  7. Autoimmune diseases (SLE, RA)

I.   Regulation Of Complement

  1. Inhibitors :
    1. Bind to complement components and halt their further action
    2. α Neuro amino glycoprotein ↓ C1 esterase
    3. S Protein ↓ C567
  2. Inactivators
    1. Destroy complement proteins
    2. Factor I ↓ C3 activation
    3. Factor H binds to C3b
    4. C4 binding protein
    5. Anaphylotoxin inactivator degrades C3a, C4a, C5a

Angioneurotic edema, what is not true? (AIIMS May 09)
A. Edema is pitting in cheeks & lips                   
B. Due to deficiency of C1 esterase inhibitor
C. Can be induced by sunlight or stress            
D. Can be caused by ACE inhibitor


Ans. A


J.   Bio Synthesis

Intestinal epithelium C1
Macrophages C2, C4
Spleen C5, C8
Liver C3, C6, C9
Not known C7

K. Genetic Deficiencies Of Complement



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