Apple and other big U.S. companies reporting fatter profits than expected are helping stock indexes shave off more of their sharp losses from the start of the week. The S&P 500 rose 0.4% at the start of trading on Friday and was on track for just a 0.

Apple stock was up in premarket trading after the iPhone maker posted first-quarter earnings results that beat expectations.

In a rare move, analysts at Jefferies downgraded one of the largest companies in the world, Apple ( AAPL -0.39%), to underperform. Wall Street analysts are known for being bullish, so underperform and sell ratings tend to make up only a small percentage of overall analyst ratings.