  The high resolution image of the jet of the BL Lac object MKN501 in radio,
show a limb-brightened feature. An explanation of this feature as an outcome of
differential Doppler boosting of jet spine and jet boundary due to transverse
velocity structure of the jet requires large viewing angle. However this
inference contradicts with the constraints derived from the high energy
$\gamma$-ray studies unless the jets bends over a large angle immediately after
the $\gamma$-ray zone (close to the central engine). In this letter we propose
an alternate explanation to the limb-brightened feature of MKN501 by
considering the diffusion of electrons accelerated at the boundary shear layer
into the jet medium and this consideration does not require large viewing
angle. Also the observed difference in the spectral index at the jet boundary
and jet spine can be understood within the frame work of shear acceleration.
