On negative(weak) reply, i.e. 1D, if opener has 16-18 pts., his rebids are natural i.e. 1S/1NT/2C/2D/2H, showing his min 5 card suit, if any, or balanced hand but if he has 19+ pts. he bids 1H i.e. Jackson Relay(irrespective of any dist.) which is an artificial bid. This is again forcing & has nothing to do with Heart suit.
On strong reply i.e. 1H (artificial) showing 12+ points, opener's rebids are natural, if he has 16-18 pts. i.e. 1NT/2C/2D/2H/2S but in case he has 19+ pts., he bid 1S which is artificial showing 19+ pts. & has nothing to do with Spade suit. Thus informing each other at one level itself that at least little slam is there.
On positive(but limited) reply, i.e. 1S/1NT/2C/2D/2H, opener's rebids are natural and continues giving natural bids till game is reached.
Note:- For higher level interference, for (i) & (iii) there will be no problem but for (ii), little judgement have to be use depending upon level of reply.