US stocks finished slightly lower on Wednesday, as polls showed the outcome of a UK referendum on whether to leave the European Union remained too close to call a day ahead of the vote. 
The S&P 500 SPX, -0.17% shed 3.45, or 0.2%, to close at 2,085.45. 
The Dow Jones Industrial Average DJIA, -0.27% fell 48.90 points, or 0.3%, to end at 17,780.83, and the Nasdaq Composite Index COMP, -0.22% dropped 10.44 points, or 0.2%, to close at 4,833.32.