Let (P_t) be the transition semigroup of a Levy process (L_t) taking values in a Hilbert space H. Let nu and (N^~) over tilde respectively be the Levy measure and compensated Poisson random measure of (L_t). It is shown that for any bounded and measurable function f, A_qP_tf(x) = 1/t E[f(L_t^x) integral(t)(0) integral(H) q(y)(N) (ds, dy)] for all t > 0, x is an element of H, where A_q is some nonlocal operator. As a corollary, integral(H) broken vertical bar P_tf(x + y) - P_tf(x)vertical bar² v(dy) <= 1/t P_tf²(x) for all t > 0, x is an element of H. As v can be infinite this formula establishes some smoothening effect of the semigroup (P_t).In the paper some applications of the formula will be presented as well.