Q.1. What is an antigen?
Ans. Antigen is a substance which when introduced into an animal can induce a detectable immune response, which may be humoral, cellular or both.
Q.2. What is the nature of an antigen?
Ans. Most antigens are macromolecules of proteins though synthetic polypeptides and certain synthetic polymers like polyvinyl pyrolidone are known to behave like antigens.
Q.3. What is meant by the term antigenic determinant and valence?
Ans. The portion of the antigen molecule which binds to its specific antibody is called the “antigenic determinant” (or “epitope”). The total number of epitopes for antigen molecule is the valence of that antigen.
Q.4. What are haptens?
Ans. Haptens are small molecules which by themselves are not capable of evoking an antibody response upon introduction into an animal. But when they are conjugated with a carrier molecule such as a protein, they behave like typical antigens.
Q.5. How the word hapten derived?
Ans. Hapten is derived from the Greek word hapten which means to fasten.
Q.6. What is understood by the term immune response?
Ans. “Immune response” may be defined as a defensive reaction by the body to the entry of a foreign substance viz. bacteria, viruses or even a foreign protein into human body.
- The immune response is a complex interplay of cells and their products. By this mechanism the organism tries to eliminate or destroy the invading foreign agent.
Q.7. What are the types of immune response?
Ans. Immune responses are of 2 types:
- Humoral immune response and
- Cellular immune response.
Q.8. What is humoral immune response?
Ans. The humoral immune response is mediated by specific protein molecules, usually γ-globulins, called antibodies or immunoglobulins (Igs); these are formed by B-lymphocytes.
Q.9. What is cellular immune response?
Ans. In cellular immune response, another type of lymphocytes called T-lymphocytes with the co-ordination with other cell systems, recognize the invading agent i.e. the antigen by virtue of certain unique molecules on their cell surface and destroy the antigen (cell-mediated immunity).
Q.10. Define immunoglobulins?
Ans. The immunoglobulins are defined to constitute a heterogenous family of serum proteins, which either function as antibodies or are chemically related to antibodies, and on electrophoresis they mainly occupy the γ-globulin position but also may occur in β-or α2-regions.
Q.11. What are the criteria laid down by WHO to call a substance immunoglobulin?
Ans. WHO’s criteria for immunoglobulins are as follows:
- Should be proteins
- Should be of animal origin
- Should have a common structure and
- Should function as antibodies.
Q.12. What is the WHO classification of immunoglobulins?
Ans. Give the corresponding old nomenclature.
Immunoglobulins (Igs) have been divided into five main classes by WHO according to the molecular weight,electrophoretic mobility, ultracentrifugal sedimentation and structural characteristics.
Classes Corresponding old nomenclatures
- IgG (γ G)— 7Sγ, γ2, γss, 6.6 sγ
- IgA (γ A)— γ1A, β2A, 7 sγ-1
- IgM (γ m)— 19 sγ, γ1m, β2M
- IgD (γ D)— —
- IgE (γ E)— —
Q.13. Why are the immunoglobulin classes and types so named?
Ans. Classes G, M, A, D and E are so named as per the nature of “heavy chains”. Thus:
- G means γ-chains (gamma)
- M means μ chains (mew)
- A means α chains (alpha)
- D means δ chains (delta)
- E means ε chains (epsilon)
Two types ‘L’ and ‘K’ stand for λ (Lambda) and κ (Kappa) light chains.
Q.14. How many immunoglobulins are there?
Ans. There are total 10 different Igs as follows:
- Five classes of Igs depending on types of heavy chains
IgG, IgM, IgA, IgD, and IgE.
- There are two types ‘L’ and ‘K’ for each class possessing
λ (Lambda) and ‘κ’ light chains. A given Ig molecule contains identical λ (Lambda) and ‘κ’ chains but never both.
- Thus, there are 5 × 2 = 10 different immunoglobulins.
Q.15. State the salient features of structure of an immunoglobulin molecule?
Ans.
- An immunoglobulin has Y-shape.
- The molecule is about 250-300 Ao long and 40 A° wide and possesses a “hinge portion”.
- Each molecule is composed of two heavy chains (‘H’-chains) and two light chains (‘L’ chains).
- Two light chains ‘κ’ (Kappa) or λ (Lambda), each of molecular weight 23,000 and consist of 214 amino acids.
- Two heavy chains γ, μ, α, δ, and ε each molecular weight 50,000 to 70,000 and consist of 446 amino acids.
- The ‘H’ chains are held together by non-covalent forces and usually covalent inter-chain disulfide bridges (Total of 3 to 4).
- The proportion of ‘κ’ to ‘λ’ chains varies from species to species being about 2:1 in humans.
Q.16. Name five antibodies contained by IgG.
Ans. The following five antibodies have been identified in this class:
- Immune anti-A and anti, B
- Anti-Rh antibodies—incomplete type
- Antiviral antibodies
- Antistreptolysin
- Auto-antibodies to thyroid
Q.17. Which immunoglobulins exist in polymeric forms?
Ans.
- IgM normally exists as pentamer
- IgA molecule also exists in polymeric forms specially as a dimer.
Q.18. What is J-chain?
Ans. J-chain is a small glycopeptide with an unusually high content of aspartic acid (Asp) and glutamic acid. It is found in each IgM pentamer or in polymeric IgA. It is claimed that J-chain facilitates the polymerization.
Q.19. Name five antibodies contained in IgM.
Ans. The following five antibodies have been identified in IgM class:
- Naturally occurring anti-A and anti-B.
- Anti-Rh antibodies-saline type
- Cold antibodies (anti-i type)
- LE factor
- Rheumatoid factor (RF).
Q.20. In the evolutionary scale, which antibody appears first in human body?
Ans. In terms of evolution, IgG claimed to have evolved later than IgM. The sequence in the animal’s response to antigenic stimulation usually consists of IgM produced initially, followed later and ultimately replaced by IgG.