According to a Mount Holyoke College webpage, some of those McCarthy accused did actually have communist sympathies. Most, however, were public figures who were Democrats or otherwise leaned to the left of the political spectrum.
Owen Lattimore and Val Lorwin were among the more high-profile individuals McCarthy accused of espionage. Lattimore was an important figure, having served as director of the Page School of International Relations at Johns Hopkins University and as editor of the Institute of Pacific Relations Journal. Lorwin, meanwhile, had worked at the State Department and was a labor economist in Paris when he was accused by McCarthy. Both men were later proven innocent, but their reputations suffered in their home country.