The batsman was controversially dropped by the ECB shortly after England's Ashes whitewash defeat to Australia Down Under in the winter.
While speaking about Pietersen's dismissal, Downton accused the cricketer of being "disinterested" in The Ashes, while also claiming that members of the senior players did not want the batsman to stay within the side.
Pietersen responded to the claims with a statement, which said: "The suggestion that I was uninterested during the winter Ashes series against Australia is wholly untrue. Although I was having injections in my knee, which inhibited my mobility and thus my ability to field close to the wicket, I was fully motivated to play for England.
"While I accept that the series as a whole fell well below my own personal standards, I finished the series as the top scorer. I did, and continue to have, a good relationship with most of the England players, which has been subsequently highlighted by a number of press interviews.
"With regard to the criticisms aimed at my 'the way I play type attitude', I feel it's only reasonable to remind Mr Downton that this method has brought me over 13,500 runs for England, in addition to being part of four Ashes-winning teams and a World T20-winning side, all of which achievements I am hugely proud of."
Pietersen has been competing for the Delhi Daredevils in the Indian Premier League.