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INE (I'm no Elder) but I have judged Nationals and so I'm using that experience to rule this how I would have if it had come up there.
I'm at work so don't have time to give an extensive ruling, but my current understanding is that you cannot be immune/protected from an ignore ability that is already in effect. Likewise, you cannot ignore a character that is already protected/immune.
I thought you cannot be immune to a character already ignoring you but you can ignore a character that is immune to you, it just results in a stalemate.
Consider that John (I) attacks. He is negating ECs (which defaults to ECs in play). King of Tyrus blocks from hand. John prevents King of Tyrus as soon as he hits the table before KoT's ability to negate John can activate. Another example would be John (I) attacks and Uzzah blocks from hand. If Uzzah's ability is allowed to activate before John can negate him, then Uzzah uses his ability and goes to the discard pile where he is no longer in play for John to negate him, which is clearly not how we've ruled it.
I see ignore as a"regardless of protection" type deal.