SSB and systemic lupus erythematosus: Autoantibodies in SLE target a 60,000 molecular-weight protein (Ro60 or SS-A) or a 48,000 molecular-weight La (SSB) autoantigen of the Ro RNP particle, associated non-covalently with one or more of four short uridine-rich human cytoplasmic RNAs (hY RNAs).