1. Online Counseling Resource YCMOU ELearning Drive… School of Architecture, Science and Technology Yashwantrao Chavan Maharashtra Open University, Nashik – 422222, India

2. © 2008, YCMOU. All Rights Reserved.2 OC-SBT091-CP1-04 Introduction Programmes and Courses  SEP–SBT091–CP1-UN-01

3. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.3 Credits  Academic Inputs by Arun Punaji More. M.Sc. (Microbiology) ‏ Experience: 11 Years arunmesh@hotmail.com

4. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.4 How to Use This Resource  Counselor at each study center should use this presentation to deliver lecture of 40-60 minutes during Face-To-Face counseling.  Discussion about students difficulties or tutorial with assignments should follow the lecture for about 40-60 minutes.  Handouts (with 6 slides on each A4 size page) of this presentation should be provided to each student.  Each student should discuss on the discussion forum all the terms which could not be understood. This will improve his writing skills and enhance knowledge level about topics, which shall be immensely useful for end exam.  Appear several times, for all the Self-Tests, available for this course.  Student can use handouts for last minutes preparation just before end exam.

5. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.5 Learning Objectives  After studying this module, you should be able to: Define the antibody diversity Describe the mechanisms of producing diverse antibodies Describe the significances of antibody diversity phenomenon

6. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.6 Introduction – One of the marvelous features immune system is its ability to produce antibodies with diverse and numerous specificities against million varieties of antigens. – Immune system in human can produce antibodies which can bind to 10 3 different antigens. – This feature gives mammals a survival advantage by resisting infections by variety of microorganisms. – It is more interesting to learn about the mechanisms of producing these diverse antibody by the immune cells. – In this module students shall learn about these mechanisms.

7. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.7 Antibody Diversity-1  To explain antibody diversity number of theories have been put forth.  Germ line theory:-  This theory state that the variety of antibodies are encoded by large number of immunoglobulin genes contributed by eggs, sperm cells and germ cells.  However the modern advances in molecular biology have proved that there are limited number of genes encoding polypeptides of antibody molecules; thus completely disproving the presence of variety of genes for production of numerous antibodies.

8. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.8 Antibody Diversity-2  Somatic variation theory:-  This theory state that genome contains small number of genes for immunoglobulins and from these small number of immunoglobulin genes number of combinations of genes are generated by the process of mutations and recombinations.  However this theory do not explain how amino acid sequences of constant regions of antibody molecules remain unchanged and highly variable amino acid sequences are generated in the variable regions of immunoglobulin molecules.

9. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.9 Antibody Diversity-3  Somatic variation theory:-  The somatic variation theory also do not explains the identical amino acid sequences in the variable regions of different classes of antibodies.

10. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.10 Antibody Diversity-4  Dreyer and Bennett’s two genes theory:-  Dreyer and Bennett proposed that there are two genes one encoding for variable region and another encoding for constant region of antibody molecule.  These two genes come together forming a continuous gene which encodes a single polypeptide heavy or light chain.  Dreyer and Bennett also proposed that in germ line there are hundred thousands copies of V- region genes and only single copy of gene for constant region of antibody molecule from its class and subclass.

11. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.11 Antibody Diversity-5  Dreyer and Bennett’s two genes theory:-  Though Dreyer and Bennett theory for antibody diversity explain variability of amino acid sequences of variable regions and conservation of amino acid sequences of constant regions, it faced stubborn resistances from the proponents of one gene one polypeptide hypothesis.  Because Dreyer and Bennett theory was explaining two genes for a single polypeptide molecule contradicting one gene one polypeptide hypothesis.  However Dreyer and Bennett could not prove their hypothesis experimentally due to lack of advanced technology of molecular biology.

12. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.12 Antibody Diversity-6  In 1976, S. Tonegawa and N. Hozumi gave direct evidence for two separate genes, one encoding for variable region and one encoding for constant region.  They also gave evidences that genes encoding for variable and constant regions get rearranged in the process of B-cells differentiation.  The development of technology of gene and protein sequencing make it possible to find out the genes encoding for polypeptide chains of immunoglobulins.

13. School of Science and Technology, Online Counseling Resource… Antibody Diversity-7 Mechanisms of antibody diversity generation:- Rearrangement of antibody genes (combinatorial joining) ‏ Generation of different condos during antibody genes splicing Somatic mutations (somatic variations) ‏

14. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.14 Antibody Diversity-8  Rearrangement of antibody genes:- – It was found that κ and λ light chains and heavy chains are encoded by different families of gene segments situated at different chromosomes. – The κ and λ light chains gene family contains three gene segments which are termed as V, J and C gene segments. – The heavy chain gene family contains four gene segments which are termed as V, D, J and C gene segments.

15. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.15 Antibody Diversity-9  Rearrangement of antibody genes:- – During differentiation of B cells, the genes segments V and J of light gene family get rearranged forming a single gene segment termed as VJ segment or VJ joint for variable region of light chain. – From the heavy chain gene family, V,D and J gene segments get rearranged forming a single gene segment termed as VDJ segment or VDJ joint which encodes for variable region of light chain. – C gene from each of these families encodes for constant region of respective light and heavy chain.

16. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.16 Antibody Diversity-10  Rearrangement of antibody genes:- – The C gene segments encoding for constant region of heavy chain are arranged sequentially in the order Cμ, Cδ, Cλ, Cε and C and expresses in that order only.

17. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.17 Antibody Diversity-11  Rearrangement of light chain genes:-

18. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.18 Antibody Diversity-12  Rearrangement of heavy chain genes:-

19. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.19 Antibody Diversity-13  Generation of different codons during gene splicing:- – Different codons are produced during joining V and J genes due to recombination events in different nucleotide sequences of V and J genes or because every recombination event between V and J genes do not take place at the same point of nucleotide sequence. – Thus while joining the V and J genes, due to recombination events at different nucleotide sequences generate further variability in Ig genes resulting in enhanced diversity in antibodies.

20. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.20 Antibody Diversity-14  Somatic mutations ( somatic variations):- – The V regions are highly prone to somatic mutations in germ line DNA during B-cells differentiation. – Such mutations introduce new variability in V regions of antibody chains.

21. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.21 What We Learn...  Meaning of antibody diversity  Different theories of generation of antibody diversity  Different mechanisms of generation of antibody diversity

22. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.22 Critical Thinking Question In a newborn baby with titre of IgM was found to be above 25 ng/dl; what are your inferences?

23. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.23 Hints For Critical Thinking Question  Only IgG antibody can pass through placenta.  Infections by viruses to fetus

24. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.24 Study Tips  Book Title: Immunology Title: Immunology Author: Author: Richard A. Goldsby, Thomas Kindt, Barbara A. Osborne. Publication: Publication: W.H. Freeman and Company, New York. Book Title: Title: Microbiology Author: Author: Prescott, Harley and Klein's Publication: Publication: McGraw-Hill international edition.

25. © 2008, YCMOU. All Rights Reserved.25 End of the Presentation Thank You !