  Using a coupling for the weighted sum of independent random variables and the
explicit expression of the transition semigroup of Ornstein-Uhlenbeck processes
driven by compound Poisson processes, we establish the existence of a
successful coupling and the Liouville theorem for general Ornstein-Uhlenbeck
processes. Then we present the explicit coupling property of Ornstein-Uhlenbeck
processes directly from the behaviour of the corresponding symbol or
characteristic exponent. This approach allows us to derive gradient estimates
for Ornstein-Uhlenbeck processes via the symbol.
