1  In some instances, siRNA also can have nonspecific effects that are not induced by its interaction with the specific target mRNA. In these cases, the siRNA molecules act non-specifically on a molecule called Toll-like receptor 3, which is an immunoregulatory “sensor” present on the cell surface. Thus, this nonspecific effect does not require the siRNA to enter the cell. Nevertheless, it can have profound consequences by activating the innate immune responses.