For decades, gay men and lesbians have been coming out of the closet in one significant arena of American life after another, except for professional team sports, says John D'Emilio, professor of gender and women's studies and history at the University of Illinois at Chicago.

D'Emilio, a pioneering historian and activist, is available to discuss the cultural and historical significance of NBA player Jason Collins becoming the first openly gay athlete from a major American team sport.

"Because of the visibility of professional sports, the decision of Jason Collins to come out and announce that he's gay is an important one," he says. "Over time, his coming out and that of others who will hopefully follow his example should have a major impact on how LGBT people are viewed throughout the United States."

D'Emilio has spent over three decades immersed in the rise of gay and lesbian issues to the center of American social and political debate. His books, one of which was cited by the Supreme Court in its landmark 2003 Lawrence v. Texas decision, are considered defining works in the field of gay and lesbian studies.

He was the founding director of the Policy Institute at the National Gay and Lesbian Task Force and was inducted into the Chicago Gay and Lesbian Hall of Fame in 2005.