NEW YORK (TheStreet) -- Stocks may have closed the day lower, but benchmark indexes did manage to generate positive returns for the month, a surprise for those who subscribe to the strategy of "sell in May and go away."

The S&P 500 closed with monthly gains of 1.1%, its best monthly gain since February. The Dow Jones Industrial Average added 1%, and the Nasdaq climbed 2.6%.

Those gains weren't felt on Friday, a session pressured by a downward first-quarter GDP revision and nerves ahead of next week's jobs report for May. The S&P 500 fell 0.63%, the Dow declined 0.63%, and the Nasdaq slid 0.55%. Economists hope to see continued strength in the labor market, proof that March's disappointing number was an aberration in a weak first quarter.

The data "will go a long way toward helping validate if the Federal Reserve is correct in its assumption that a lot of the things that negatively impacted the first quarter were transitory," said Eric Wiegand, senior portfolio manager at U.S. Bank, in a call.

Economists expect the economy to add 210,000 jobs in May with the unemployment rate remaining unchanged at 5.4%. Hourly earnings are forecast to increase 0.2% month on month. The Labor Department will release the data on Friday, June 5.

First-quarter gross domestic product, originally seen up 0.2%, was revised down to negative 0.7% in a second estimate. The contraction was slightly narrower than economists had expected, though marked a stark reminder of how bad economic growth truly was at the start of the year.

The value of inventories increased by $95 billion, down from a previously estimated increase of $110.3 billion. Exports fell 7.6%, while imports were revised up to 5.6% from 1.8%, leading to a larger trade deficit which reduced GDP.

Economists expect the economy to bounce back in the latter half of the year, and second-quarter data including monthly housing figures support this. Second-quarter GDP is expected to rise 3%.

"Second estimates of GDP are generally "old news" and today's report falls along those lines," said BTIG Research chief strategist Dan Greenhaus. "The Fed, market participants and just about everyone believes first-quarter issues were transitory in nature and as such, a revision into negative territory is unlikely to affect the broader debate."

Humana (HUM) was the best performer on the S&P 500, jumping 20.1% following a report in The Wall Street Journal that the health insurer was considering a sale.

American Express (AXP) President Ed Gilligan died on Friday after becoming suddenly ill on a flight to New York. American Express Chairman and CEO Kenneth Chenault broke the news in a letter to employees and contractors.

United Rentals (URI) dropped after analysts at Bank of America downgraded the equipment rental company to "underperform" from "neutral." Analysts said pricing power continues to be pressured by the collapse in crude oil prices. Click here for more.

Intel (INTC) was higher after reportedly nearing a deal to buy Altera (ALTR), according to the New York Post, adding further fuel to reports of deal negotiations between the two companies. Intel could offer Altera $15 billion, a deal that would value Altera shares at $54, a 15% premium to Thursday's close. Click here for more (paywall).

Syngenta (SYT) shares were on watch as the company reportedly builds its defenses against another potential takeover bid from Monsanto (MON). The agricultural company had added UBS as its adviser alongside Goldman Sachs as it prepares for a higher bid than the $45 billion offer it previously rejected.

On the earnings calendar in the week ahead, Dollar General (DG) and Guess? (GES) will report on Tuesday, Five Below (FIVE) and Vera Bradley (VRA) are set for Wednesday, and Joy Global (JOY) and J.M. Smucker (SJM) are scheduled for Thursday. 

Aside from Friday's jobs report, personal income for April and the ISM Manufacturing Index for May will be released on Monday, April factory orders will be released Tuesday, and the trade balance for April will be released Wednesday. The Fed's Beige Book, an anecdotal report of the 12 Federal Reserve districts, will be released on Wednesday afternoon. 

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