common collector amplifier
I thought common collector amplifier is immune to loading effects


A CC is not immune to loading since it has a low, but non-zero, output impedance.

The small signal output impedance of a CC amplifier is roughly:

\$\dfrac{V_T}{I_E} + \dfrac{R_{tb}}{\beta + 1}\$

where

\$V_T \approx 25mV \$ (assuming room temperature)

and \$R_{tb}\$ is the equivalent AC resistance connected to the base.

For example, if \$I_E = 1mA\$, the output impedance is at least 25 ohms. 

So, while the output impedance of a CC amplifier is much lower than a CE amplifier, it is not immune to loading effects.