The neutrino spin kinetic equation in a medium with a magnetic field i
s derived, with the inclusion of the self-consistent electromagnetic f
ield in a plasma. In order to check the proposed approach we reproduce
the known results for the Dirac neutrino helicity change in constant
and twisting magnetic fields. The new neutrino helicity change channel
affected by the linear-polarized Alfven wave of a finite amplitude pr
opagating along the general magnetic field Bo is considered. In contra
st with the known cases, this channel arises for the longitudinal neut
rino propagation p parallel to B-0, where p is the neutrino momentum.