Systems Microbiology 1.084J/20.106J PROBLEM SET #6 – Due Wednesday Dec. 6 th 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. Problem 6.2 a. List and describe the important steps in selection and activation of a T-cell. Why are each of these
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