Anti-Th/To Antibodies

SARDs are a heterogeneous group of disorders characterized by dysregulation of the immune system, that starts to turn against the body’s own tissues. Major SARDs include systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis and Sjögren’s syndrome. These diseases can affect multiple organs and share common symptoms such as fatigue, fever, joint pain and skin rash. Diagnosis relies on a combination of clinical assessment and specific autoantibody tests. Early diagnosis is crucial to initiate appropriate therapy and slow down disease progression.

The target antigen of anti-Th/To autoantibodies is the RNase MRP (mitochondrial RNA processing) macromolecular complex, a ubiquitous endoribonuclease involved in the specific processing of ribosomal, messenger and mitochondrial RNA. This complex consists of a catalytic RNA component and at least nine proteins, among which Rpp25, Rpp38 and hPop1 have been identified as the main autoantigens recognized by anti-Th/To antibodies.

Anti-Th/To antibodies are rare, with an estimated prevalence of 2–5% in patients with systemic sclerosis (SSc), and are predominantly associated with the limited cutaneous form of SSc (lcSSc). Despite their low frequency, their clinical significance is high as they identify specific patient subgroups.