CHICAGO--(BUSINESS WIRE)--Fitch Ratings has upgraded four classes and affirmed 12 classes of Bear Sterns Commercial Mortgage Securities Inc. commercial mortgage pass-through certificates series 2005-TOP18. A detailed list of rating actions follows at the end of this press release. KEY RATING DRIVERS The upgrades and affirmations reflect continued paydown and increasing credit enhancement as well as the significant paydown expected from upcoming maturities in the first half of 2015. Fitch modele