Papachristou, 23, was preparing to head to London for her first Olympic Games when she posted a joke to her Twitter feed. It was about the West Nile virus, and appeared to mock Greece's African immigrant population.
"With so many Africans in Greece, at least the mosquitoes of West Nile will eat homemade food!!!" she tweeted Sunday.
Papachristou has often taken to Twitter to express her support for the extreme right-wing party Golden Dawn, which has recently surged in popularity among Greeks.
In response to criticism by Twitter users who said her joke was racially insensitive, she initially took a defiant tone.
"I'm not a stuck CD! And if I make mistakes, I do not hit replay! I continue playing!" she tweeted on Monday.
By Wednesday, though, she had turned remorseful, saying in a statement on Twitter and Facebook, "I would like to express my heartfelt apologies for the unfortunate and tasteless joke I published on my personal Twitter account. I am very sorry and ashamed for the negative responses I triggered, since I never wanted to offend anyone, or to encroach human rights."
"I would like to apologize to all my friends and fellow athletes, who I may have insulted or shamed, the National Team, as well as the people and companies who support my athletic career," she said. "Finally, I would like to apologize to my coach and my family."
That apology was not enough to save her spot on the Greek Olympic team. The Hellenic Delegations' Administration Board decided to remove her from the team, citing "comments that go against the values and ideals of Olympism."
In Greece, reactions to the tweet and Papachristou's expulsion appeared to split along partisan lines. A spike in illegal immigration from Africa and Asia has contributed to increasing anti-immigrant sentiment among many Greeks.
The co-ruling Democratic Left party joined the chorus calling for Papachristou's expulsion.
"She can make as many vile 'jokes' as she likes on social-networking sites when she watches the Olympic Games on TV," it said. "But she certainly cannot represent Greece in London."
Papachristou's coach, George Pomaski, told Reuters the expulsion was an overreaction, especially considering Papachristou's apology.
"It's too much, the penalty should not have been so strict," Pomaski told Reuters. "This is a big disappointment not only for her but for her family and for myself and anyone involved in the Greek team."
Meanwhile, supporters in Greece and abroad have flocked to social-networking sites to defend Papachristou, who finished 11th in June's European championships in Helsinki with a 13.89-meter jump but did not reach the 2011 world championship final.
"Anybody who watches 'Family Guy' probably found the joke funny. Anyone offended took it the wrong way," said Ryan Brenneman of Marion, Ind., on Papachristou's Facebook page. "I'm sorry it blew up on you. It's a shame that you worked so hard and can't compete now...."
Another American commenter said comedians on national television in the United States could have made the same joke with "absolutely no consequences to them."
While many argued that the tweet was misinterpreted or simply not offensive, others said Papachristou should be forgiven because she has apologized for her mistake.
Papachristou's apology quickly garnered more than 800 "likes," and Facebook groups calling for her reinstatement on the team are proliferating.
"You have obviously worked your entire lifetime to get where you are today and that should not all be taken away from you for a single NOT at all severe comment," said Ava Scofiled, of Monterey, Calif., in a letter she posted to one of those groups.