  The proton-proton bremsstrahlung is investigated within a coupled-channel
model with the $\Delta$ degree of freedom. The model is consistent with the
$NN$ scattering up to 1 GeV and the $\gamma N\Delta$ vertex determined in the
study of pion photoproduction reactions. It is found that the $\Delta$
excitation can significantly improve the agreements with the $pp \rightarrow
pp\gamma$ at $E_{lab}=280$ MeV. Predictions at $E_{lab}=550$ and $800$ MeV are
presented for future experimental tests.
