ps6_sol - Solutions Systems Microbiology 1.084J/20.106J...

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Solutions Systems Microbiology 1.084J/20.106J PROBLEM SET #6 Problem 6.1 Shiga toxin (Stx) is a potent A-B toxin that inhibits protein synthesis and has a lethal dose 50* (LD 50 ) of approximately 20 ng/kg of body weight in rabbits (meaning that 1 μg of Stx would be lethal for half the people exposed to this dose). Nonetheless, cell lines derived from different mammalian tissues range from highly susceptible (cytotoxic dose 50 [CD50] of approximately 10 pg/ml) to completely resistant (CD50 > 1 μg/ml). What cellular or molecular differences do you think account for susceptibility and resistance of these cell lines. How could you test your hypothesis? *LD 50 is the dose at which 50% of the test subjects die. In this case, it was determined for rabbits given intravenous injections of the toxin. CD 50 is the concentration at which 50% of the cells die. Different cell lines from different tissues will or will not express the receptor for the B subunit of the toxin. Without receptor expression the A subunit of the toxin will not get transported into the cytoplasm where it will be able to inhibit protein synthesis. This can be tested by administering the B subunit alone or the A subunit alone to determine the susceptibility of each cell line. Could also test for Gb3 content of the cells. Problem 6.2 a. List and describe the important steps in selection and activation of a T-cell. Why are each of these steps important and what would be the consequences if they did not occur? Positive selection—T cells that DO interact with MHC proteins in the thymus divide and proliferate.
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ps6_sol - Solutions Systems Microbiology 1.084J/20.106J...

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