  In this paper we discuss the anti-GZK effect that arises in the framework of
the diffusive propagation of Ultra High Energy (UHE) protons. This effect
consists in a jump-like increase of the maximum distance from which UHE protons
can reach the observer. The position of the jump is independent of the
Intergalactic Magnetic Field (IMF) strength and depends only on the energy
losses of protons, namely on the transition energy from adiabatic and
pair-production energy losses. The Ultra High Energy Cosmic Rays (UHECR)
spectrum presents a low-energy steepening approximately at this energy, which
is very close to the position of the observed second knee. The dip, seen in the
universal spectrum as a signature of the proton interaction with the Cosmic
Microwave Background (CMB) radiation, is also present in the case of diffusive
propagation in magnetic fields.
