The Los Angeles Business Journal’s index of largest local public companies gained for the week as the broader markets reacted to the Federal Reserve’s stimulus package.

The weighted LABJ Stock Index closed up 1.7 percent to 141.52 for the week ended Sept. 14. Gainers outpaced decliners 115 to 54, with seven companies unchanged.

The biggest gainer was Response Genetics Inc., which soared 75 percent to $1.35. The Los Angeles diagnostic test developer said it raised $8.8 million in a private placement of its stock, mostly acquired by British drug maker GlaxoSmithKline Plc.

Virco Mfg Corp. jumped 72 percent to $2.75. The Torrance institutional furniture maker reported a 163 percent higher second-quarter net income on improved gross margins.

NetSol Technologies Inc. gained 19 percent to $5.73. An analyst upgraded the stock of the Calabasas company, which makes corporate credit and finance management software, following a better-than-expected fiscal fourth quarter report.

American Apparel Inc. rose 18 percent to $1.39. The downtown L.A. clothing manufacturer and retailer announced a rise in monthly sales and an extension of a previous credit agreement.

Among the biggest decliners was Los Angeles specialty soda maker Reed Inc., which fell 12 percent to $6.13 despite the lack of market-moving news.

THQ Inc. fell 7 percent to $4.09, as analysts believed that the success of the Agoura Hills video game maker’s “Darksiders II” wasn’t going to be enough to solve the company’s problems.