Paul Boulis is retiring as president of Blue Cross and Blue Shield of Illinois, the state's largest health plan. Boulis, 59, will step down effective Dec. 31 after 25 years with Illinois Blue Cross, a subsidiary of Chicago-based Health Care Service Corp. He will be replaced by another Illinois Blue Cross veteran, Karen Atwood, 53, senior vice president of the company's national division, which manages more than 350 major national, municipal, and labor accounts. Under Boulis, Illinois Blue Cross grew to more than 7 million health plan subscribers and 30,000 employer groups. Like Atwood, he spent much of his career overseeing the important national accounts business, which is designed to cover employees at large multi-state employers.