What is the difference between P155/140 and TIF1-γ antibodies on the ARUP myositis panel?

TIF1g is the name of the protein itself, whereas "p155/140" refers to the IP (immunoprecipitation) finding of 2 distinct bands at 155 kDa (TIF1g) and 140 kDa (TIF1a), indicative of an anti-TIF1g antibody response. Until recently, ARUP (like most commercial laboratories) used immunoblotting, as it is fast, simple, and automated, but it has low specificity for TIF1g. They have since switched to PMAT (particle-based multianalyte technology, reported as TIF1g) and also offer IP (reported as p155/140...