PITTSBURGH -- The Pittsburgh Steelers have gotten younger on defense, but they are still relying on a trio of players who were cornerstones of the teams that played in three Super Bowls from 2005-10.

Outside linebacker James Harrison is already playing significant snaps even though the 36-year-old is still working his way into football shape. Defensive end Brett Keisel, who is also 36, leads the Steelers with 10 quarterback pressures and is playing over Cam Thomas in the nickel package.

And then there is Troy Polamalu, the pup, if you will, of the trio.

The veteran strong safety is third on the Steelers with 31 tackles, and the eight-time Pro Bowler has gotten better with each game. Polamalu, at the age of 33, is not the disruptive force he had been while winning the NFL Defensive Player of the Year award in 2010.

But Steelers defensive backs coach Carnell Lake sees Polamalu producing the big plays that have been his hallmark -- and doing it in bunches at some point this season.

“One thing I found out about Troy is just when you think, ‘Oh, he’s not really going to [do] that much this year,’ boom, he starts making plays just like he did last year,” Lake said. “He’s building. It’s like our team in general. The gears are turning.”

Harrison is the most unlikely of those gears.

Keisel and Polamalu helped talk Harrison out of retirement after starting outside linebacker Jarvis Jones went down in a 37-19 win over the Carolina Panthers last month with a dislocated wrist.

Harrison played almost 30 snaps in his first game back with the Steelers and 20 in the 17-9 win at Jacksonville last Sunday. Harrison dropped Jaguars running back Denard Robinson for a 2-yard loss the play before cornerback Brice McCain returned an interception for a touchdown.

“I’m not where I want to be right now but week in, week out it gets a little better,” Harrison said Thursday before practice. “We’ll see how far and how fast I progress.”

When asked if he is progressing slower than he had anticipated, Harrison said with his typical bluntness, “If you were trying to lose weight, you’re not going to lose all the weight you want to in two weeks are you? It takes time.”

Despite the process of working his way back into shape and playing a supporting role on defense, Harrison said he doesn’t regret coming out of retirement, even though he had been content to walk away from the game.

"Everything happens for a reason,” Harrison said. “I’m here because that’s what was meant to be. It’s the right decision.”