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Everything you need to know about immunology. Some of the frequently asked questions are as follows:-
Q.1. What is immunology?
Ans. Study of a host’s specific defense to a pathogen or a foreign substance is called immunology.
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Q.2. What is an antigen?
Ans. A substance which on entering a body causes formation of antibodies and reacts only with a specific antibody is called antigen.
Q.3. What is an antibody?
Ans. A protein formed by the body in response to an antigen and is capable of combining specifically with that antigen often leading in vivo to its destruction or inactivation.
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Q.4. What is acquired immunity?
Ans. It is the protection which an animal (vertebrate) develops over a period of time against certain types of microbes or foreign substances.
Q.5. Give types of acquired immunity.
Ans. There are two main types of acquired immunity:
(1) Naturally acquired and
(2) Artificially acquired.
(1)Naturally acquired immunity further consists of two types:
(a) Natural Active immunity, in which antigens enter the body naturally, and the body produces antibodies and specialized lymphocytes,
(b) Naturally acquired Passive immunity, as the antibodies pass from mother to foetus via placenta or to the infant through her milk.
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(2)Likewise, artificially acquired immunity also is of two types:
(a) Artificially acquired active immunity, e.g., the antigens are introduced in vaccines. The body produces antibodies and specialized lymphocytes,
(b) Artificially acquired passive immunity, and e.g., preformed antibodies in immune serum are introduced into body by injection.
Q.6. What is colostrum?
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Ans. The first secretion of breast milk of mammals after birth of infant. It helps to establish natural active immunity.
Q.7. What is serum (plural sera)?
Ans. The remaining fluid after the blood has clotted or coagulated.
Q.8. What is immune serum globulin or gamma globulin?
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Ans. On subjecting the serum to an electric current during electrophoresis the proteins in it move at different rates. One of the components separated in this way contains most of the antibodies. This antibody rich component of serum is called immune serum or gamma globulin.
Q.9. What is humoral immunity?
Ans. It is an antibody mediated immune system found in vertebrates.
Q.10. Which cells of the blood are responsible for production of antibodies?
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Ans. B-cells or B-lymphocytes.
Q.11. Production of which types of cells is involved in cell mediated immunity?
Ans. Specialized lymphocytes called T-cells or T-lymphocytes.
Q.12. What are epitopes?
Ans. The epitopes are specific regions on the surface of an antigen against which antibodies are formed.
Q.13. Name the common antigens.
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Ans. These are proteins or large polysaccharides. The lipids and nucleic acids often are antigenic only when combined with proteins and polysaccharides. The antigenic components are often components of invading microbes, e.g., capsules, cell walls, flagella, fimbriae and toxins of bacteria, protein coats of viruses, and surface of other types of microbes. Pollen grains, egg white, blood cell surface molecules, serum proteins from other individuals or species and surface molecules of transplanted tissues and organs are the examples of non-microbial antigens.
Q.14. What are the substances against which specialized B-cells defend in humoral or antibody mediated system?
Ans. Extracellular bacteria, bacterial toxins and viruses.
Q.15. Which are the substances against which T-cells defend in cell mediated immune systems?
Ans. Intracellular bacteria and viruses, fungi, protozoa, helminths, transplanted tissue and cancerous cells.
Q.16. What are haptens?
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Ans. These are very small molecules which are not antigenic by themselves but work as an antigen on combining with larger carrier molecules, e.g., penicillin works as a Hapten and combines with serum proteins causing allergy to some people.
Q.17. Which are the five classes of immunoglobulin’s?
Ans. The five classes of immunoglobulin’s (Igs) are IgG, IgM, IgA, IgD and IgE.
Q.18. What is common and similarity in structure of Ig G, Ig D and Ig E?
Ans. They are monomers.
Q.19. How are the structures of Ig M and Ig A closely related?
Ans. Both of them comprise two or more monomers joined together by mono-sulphide bonds. Ig M is a pentamer while Ig A is a dimer.
Q.20. Which is the most common of all immunoglobulin’s?
Ans. Ig G, which has 80% of all antibodies in serum.
Q.21. How does Ig G provide passive immunity to a foetus (fetus)?
Ans. They being monomer, readily cross the walls of blood vessels and also cross the placenta.
Q.22. Why does Ig M often remain inside blood vessels?
Ans. Their large size (Ig M from macro means large) prevents moving about as freely as Ig Q and does not enter the surrounding tissue of blood vessels.
Q.23. Where does Ig A (also called Secretory Ig A) generally occur?
Ans. It occurs in secretions such as tears, saliva, mucous, intestine and milk. However, it also occurs in blood and lymph.
Q.24. How does occurrence of T-cells and B-cells differ?
Ans. The lymphocytes T cells and B cells originate from stem cells in adult bone marrow or in fetal liver. It is important to note that red blood cells, macrophages, Neutrophils and other white blood cells also originate from these same stem cells. Some cells pass through the thymus and form into as mature T cells. The other cells remain in the bone marrow and become B cells. Both types of cells then migrate to lymphoid tissues, i.e., lymph nodes and spleen.
Q.25. How do B cells recognize antigens?
Ans. B-cells can recognize antigens by antigen receptors present on their surfaces.
Q.26. What is clonal selection in activation of antibody producing cells?
Ans. When an appropriate antigen binds to the antigen receptors of B-cells, the B-cells proliferate into a large clone of cells which is referred to as clonal selection.
Q.27. How many molecules of antibody are produced by each plasma cell which live for a few days?
Ans. 2000 molecules per second.
Q.28. The B and T cells that interact with self antigens are destroyed during fetal development. What is it called?
Ans. Clonal deletion.
Q.29. What is immunological memory?
Ans. The second response to an antigen is called immunological memory or anamnestic response.
Q.30. What are memory cells?
Ans. Some activated B lymphocytes do not result into antibody producing plasma cells. They rather persist as long-lived memory cells for many years.
Q.31. What is hybridoma?
Ans. Hybridoma is a clone of cells produced from the fusion cell. It is formed as a result of fusion of the antibody producing B-cell with a cancer cell.
Q.32. What is CD type of T-cells?
Ans. Cluster of differentiation.
Q.33. What are two types of CD receptors?
Ans. CD4 and CD8 cells.
Q.34. What are CD4 cells?
Ans. The CD4 cells are helper T cells (which also work as receptors of HIV in causation of AIDS).
Q.35. What are CD8 cells?
Ans. They are cytotoxic and suppressor T cells.
Q.36. What is septic shock?
Ans. Sudden drop in blood pressure due to infection by Gram-negative bacteria (even infection due to cell walls of population of Gram-negatives killed by antibiotics).
Q.37. What are helper T or (TH) cells?
Ans. Specialized T cells that generally interact with an antigen before B-cells start to interact with the antigen.
Q.38. What are cytotoxic T (Tc) cells?
Ans. These are specialized T- cells which destroy infected cells possessing antigens. Therefore, they provide protection against viral infections and intracellular bacterial infections.
Q.39. What are delayed hypersensitivity T (TD) cells?
Ans. These are specialized T-cells which produce lymphokines in type IV hypersensitivities. They are therefore, associated with certain allergic reactions. TD cells are the cells from which cell- mediated immunity was originally named.
Q.40. What are suppressor T (Ts) cells?
Ans. Ts cells are the cells which are believed to end an immune response after an antigen is no longer present.
Q.41. Give the diversity of antibodies?
Ans. The antibodies are proteins when introduced into an animal for which they are foreign they like any other protein induce the formation of antibodies that may be called antiantibodies. So the antibodies can also work as antigens.
Their 3 main types are isotypes, allotypes and idiotypes:
1. The human immunoglobulin’s while injected into rabbit, are recognized as foreign bodies by the rabbit. The rabbit antiserum precipitates with a number of distinct components in human serum. Each of the line of precipitate is called an isotype (iso = same). The dominant isotype is IgG.
2. The antibody allotypes (all = other) are genetically distinct types of antibody molecule which are found in some members of a species but not in others. They are inherited as simple Mendelian traits, e.g., rabbit IgG molecules exist in two allotypic forms, d11 and d12.
3. An idiotype (idio = one’s own) is usually found only on that subset of antibodies that share an identical antigen binding site. Niels Jerne in 1973 proposed a conceptual theory called the network theory which predicted the consequences of immune-system recognition of self-antibody, for which Jerne was awarded Nobel Prize in 1984.
According to the network theory as antibody is produced in response to an antigen it in turn induces the formation of antibodies to its unique variable region sequences. Jerne called each of the individual antigenic determinants of the variable region as an idiotope. Each antibody contains multiple idiotopes and sum of the individual idiotopes is known as an idiotype of the antibody.
Q.42. Give a regulatory mechanism of expression of MHC Genes.
Ans. Although it is the beginning of research in this area yet it has been revealed that both class I and class II MHC genes are flanked by 5′ promoter sequences that bind sequence specific transcription factors. The transcriptional regulation of MHC is mediated by both positive and negative elements. The MHC II trans-activator referred to as CIITA and another transcription factor known as RFX have been noticed to bind the promoter region of class II MHC genes.
A fault with these transcription factors cause a form of bare lymphocyte syndrome. The patients of this category do not have class II MHC molecules or their cells, therefore, suffer a great immunodeficiency since class II MHC molecules play a central role in maturation and activation of T-cells.
Besides the gene regulation the expression of MHC molecules is also regulated by various cytokines and interferon’s and tumor necrosis factors each of which lead to increase of class I MHC molecules on the cells. The MHC expression is also increased or often decreased by some viruses as human cytomegalovirus (CMV), hepatitis B (HBV) and adenovirus 12 (Ad 12).
Q.43. Which are the autoimmune diseases mediated by direct cellular damage?
Ans. The autoimmune diseases which are caused when lymphocytes or antibodies bind to cell membrane resulting into cellular lysis or an inflammatory response, which are given below:
1. Hashimotos thyroiditis, is seen in middle aged woman leading to formation of goiter and visible enlargement of thyroid gland, because of production of auto-antibodies and sensitized TDTH cells.
2. Autoimmune anemia, is caused when auto-antibodies bind to intrinsic factor (membrane bound intestinal protein) blocking the intrinsic factor mediated absorption of vitamin B12 from small intestine. It can be treated by injecting vitamin B12.
3. Good-pasture’s syndrome, is caused because of binding of basement membrane antigens to basement membranes of kidney glomeruli and alveoli of lungs leading to damage of kidney and haemorrhage in lungs.
4. Insulin-dependent diabetes mellitus, which is caused because of an autoimmune attack against insulin producing beta cells.
Q.44. What is a Vaccine?
Ans. A vaccine is an antigenic preparation administered in order to stimulate the recipient’s protective immunity to one or more particular pathogens and/or toxins. Some vaccines e.g., Sabin vaccine (anti-poliomyelitis) are given orally, others e.g. BCG are given parenterally. To be effective a vaccine must stimulate the formation of antibodies in part of the body where they can efficiently counteract infection.
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There are six main types of vaccines:
(a) Inactivated vaccines e.g. those used against cholera and typhoid.
(b) Attenuated vaccines e.g. Those used against tuberculosis and yellow fever.
(c) Toxoid e.g. in the triple vaccine.
(d) Solutions or suspensions of antigenic extracts from specific pathogens e.g. polysaccharide capsular material from Streptococcus pneumonia.
(e) Synthetic vaccines e.g. synthetic peptides antigenic determinants of the pathogen/ toxin, e.g. foot and mouth disease, influenza virus and Plasmodium.
(f) Genetically engineered vaccines, e.g. vaccine virus.
Q.45. What are Precipitation Reactions? Explain
Ans. The precipitation reactions occur as an interaction between an antibody and an antigen in aqueous solution forming a lattice which develop into a visible precipitate. The antibodies which aggregate soluble antigens are referred to precipitins. The precipitation reactions can also be used as a rapid test for the presence of antibody or antigen.
The interfacial (ring) precipitin test is done by adding antiserum to a small tube and layering antigen on the top. The formation of a visible line of precipitation in the tube is indicative of positive reaction. The precipitation reactions may also be in the gels. These immunodiffusion reactions can be used to determine relative concentration of antibodies or antigens.
The immunodiffusion techniques are of following types:
1. Radial immunodiffusion or Mancini method which is routinely used to serum levels of IgM, IgG and IgA. But this method cannot detect antigens concentration below 5- 10 µg/ml.
2. Double immunodiffusion or Ouchterlony method in which both antigen and antibody diffuse radially from wells towards each other distinguish each other establishing a concentration gradient. The pattern of lines drawn or concluded from possible precipitin pattern indicates whether the two antigens have identical isotopes (identity), partially identically epitopes (partial identity) or no epitopes in common (nonidentity).
3. Immunoelectrophoresis, which is often used in clinical laboratories to detect the presence or absence of proteins in the serum.
4. Rocket electrophoresis in which the precipitate formed between antigen and antibody appear in the shape of a rocket. This technique gives quantitation of antigen levels as low as 0.2 µg/ml.
