Meanwhile, in a skillet over low heat, melt butter. Stir in flour, salt and pepper until smooth. Gradually stir in milk. Bring to a boil; boil and stir for 2 minutes or until thickened. Remove from the heat. Combine cheeses; toss with lemon juice. Add to the sauce; stir until cheese begins to melt. Drain linguine; add the cheese sauce and toss to coat.