'Blind Side' Actor Quinton Aaron on Life Support, Partially Breathing, Gives 'Thumbs Up'

3:20 PM PT -- Quinton Aaron's wife Margarita tells TMZ ... "He opened his eyes today and gave a thumbs up."

Quinton Aaron -- the actor who played Michael Oher in "The Blind Side" -- is on life support after being hospitalized following a collapse at his home ... but there are some positive signs for his recovery.

Quinton's wife, Margarita, tells TMZ ... the medical devices helping keep Quinton alive aren't doing all the work, and he's partially breathing on his own, which gives the family hope.

We're told Quinton's been hospitalized for 4 days now ... and with each passing day, he shows more signs of improvement.

Quinton's wife says he has a blood infection and doctors are still running a battery of tests to determine the source of the issue.

Margarita tells us her husband woke up one morning feeling sore but thought it was from a bad sleep ... a few days later, with pain still in his neck and his back, Quinton was walking up the stairs when he lost feeling in his legs.

Quinton's wife, who is a registered nurse, says she rushed to his side and helped him up the stairs ... he laid down, and she called 911 ... with Quinton slipping in and out of consciousness on his way to the hospital, where doctors recommended life support.