A 50-year-old male patient presented with weakness of B/L lower limbs which was symmetrical (distal weakness>> proximal muscle weakness) for 1 month. On examination, ceain skin and nail changes were noted. Patient also complained of myalgia and ahralgia. Lab findings, Raised creatinine kinase levels Raised ANA antibody titre Muscle biopsy was done from the quadriceps femoris muscle. CD4+ cells were found in the cellular infiltrate. IHC study of which protein is a very sensitive diagnostic test for the above condition: -