pset8S - Solution Key - 2010 7.012 Problem Set 8 Question 1...

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1 Solution Key - 2010 7.012 Problem Set 8 Question 1 You have purified a novel protein, which you call Protein R as a part of your summer project. You would like to further characterize this protein. Accordingly, you want to develop antibodies against this protein. You inject Protein R into a rabbit and after one month you draw some blood from this rabbit and determine that the rabbit’s immune system has developed antibodies against Protein R. You wait for one month and then inject Protein R again into the same rabbit. You observe a stronger secondary immune response developing within a few days against Protein R. a) On the graph below, draw the primary and secondary immune responses of the rabbit against Protein R. b) Why is the secondary immune response faster and stronger compared to the primary immune response? During the primary immune response, the memory B cells, against the specific antigen, are generated. These B cells express surface IgM molecules against the specific antigen. Furthermore, they can also proliferate to form more memory B cells and plasma cells that produce the IgG antibody to counteract the antigen infection. During the secondary immune response, the memory B cells generated during the primary immune response immediately start proliferating to generate more of their own kind and also the IgG producing plasma cells to counteract the viral infection thus making the response faster and stronger compared to primary response. c) Which two classes of B cells in the immune system produce antibodies during the primary and secondary immune responses? B cells (both memory B cells and plasma B cells) produce antibodies against the foreign antigen. d) The immune system’s first encounter with an antigen is via the IgM class of antibodies. Once the response is initiated, the immune cells produce the IgG class of antibodies that circulate in the blood stream. You isolate the antibodies produced against Protein R, resolve them on a protein gel based on their molecular weight and obtain a profile as shown in the schematic below. i. Identify the two classes of antibodies in lane 1 and lane 2 of the protein gel. Lane 1 of the protein gel. IgG Lane 2 of the protein gel. IgM ii. Do the two classes of antibodies have … identical or different antigen binding sites? same number of antigen binding sites (Yes/No)? Explain . It has different number of antigen binding sites. Since IgG is monomer it has 2-antigen binding sites/IgG molecule in comparison to 10 binding sites/ IgM molecules, which is a pentamer. 1 2 Higher molecular weight Lower molecular weight Protein gel Antibody Titer Time ( weeks) Primary response Secondary response 1 st injection 2 nd injection
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2 Question 1, continued e) Towards the end of the primary and / or secondary immune response, you incubate the two cell- types that you have identified in part d(ii) with a fluorescent dye (Annexin V). This dye specifically binds to terminally differentiated cells that are undergoing apoptosis. You then sort the cells using a
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pset8S - Solution Key - 2010 7.012 Problem Set 8 Question 1...

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