Interferons

An important antiviral system is provided by the interferons (Table 5.5 and Fig. 5.4). The interferons are peptides that, when viral infection occurs, carry out three distinct functions. First, they send a signal to a natural killer cell that essentially leads to the self-destruction of the infected cell. Second, they induce an antiviral state in neighboring cells, limiting the viral infection. Third, when interferon receptors are bound on a target cell, the induction of the formation of antiviral proteins occurs. One such protein is the enzyme 2',5'-oligoadenylate synthetase. This enzyme catalyzes the reaction that converts ATP into 2',5'-oligoadenylate. This compound activates ribonuclease R, which possesses the specificity to hydrolyze viral RNA and thus can stop propagation of the virus inside the cell.

Acquired (Adaptive) Immunity

When the host is exposed to an antigen or organism that has been contacted previously, the adaptive immune response ensues. The adaptive immune response works through the B and T lymphocytes, which possess surface

TABLE 5.5 Interferons

Interferon Producing Cells Producing Mechanism Isotypes Molecular Mass Receptor

TABLE 5.5 Interferons

Interferon Producing Cells Producing Mechanism Isotypes Molecular Mass Receptor

Type 1

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