Final answer:
Option d. increased response of T-cells to antigens is not a typical effect of aging on the immune system.
Step-by-step explanation:
Of the options listed, option d. increased response of T-cells to antigens is not a typical effect of aging on the immune system. As people age, the immune system naturally becomes less effective, leading to a decrease in size and viability of the thymus gland (option a), increased susceptibility to infection (option b), decreased response to vaccines (option c), and decreased production of antibodies (option e).