Moody's Investors Service adjusted ratings on most tranches within 51 residential mortgage-backed securities (RMBS) worth nearly $19.64bn and backed by prime jumbo and Alt-A mortgages. The moves come as loss expectations on Alt-A and prime jumbo pools issued from 2005 to 2008 continue to evolve. The credit-rating agency downgraded ratings on 245 tranches, confirmed ratings on 10 tranches and upgraded two other tranches within 12 prime jumbo RMBS deals worth $8.1bn and issued by Wells Fargo Mortgage-Backed Securities from 2005 to 2007. Moody's downgraded ratings on 228 tranches, confirmed ratings on 15 tranches and upgraded six tranches within 20 prime jumbo RMBS deals worth $6.2bn and issued by Citicorp Mortgage Trust from 2005 to 2008. The agency downgraded ratings on 32 tranches and confirmed another tranche within three prime jumbo RMBS deals worth $537m and issued by PHH from 2005 to 2008. Additionally, Moody's downgraded ratings of 122 tranches, confirmed 8 and upgraded one other tranche from 16 Alt-A RMBS deals worth $4.8bn and issued by Structured Adjustable Rate Mortgage Loan Trust in 2005. The ratings actions arrive after Moody's recently downgraded 98 tranches of jumbo RMBS deals worth $10.5bn and issued by Wells Fargo (WFC) between 2005 and 2008. Write to Diana Golobay. Disclosure: the author holds no relevant investments.