Some creatures are immune to certain effects. If a creature is immune to a damage type (such as cold or fire), it doesn’t take that type of damage. If a creature is immune to charm, fear, illusion, or poison, it is unaffected by the non-damaging effects of a power that has that keyword. A creature that is immune to a condition or another effect (such as the dazed condition or forced movement) is unaffected by the stated effect.
    Immunity to one part of a power does not make a creature immune to other parts of the power. For example, when a creature that is immune to thunder is hit by a power that both deals thunder damage and pushes the target, the creature takes no damage, but the power can still push it.

Published in Rules Compendium, page(s) 225.