Soluble Programmed Death 1 (sPD1) is a Diagnostic Biomarker of ILD in Patients With Rheumatoid Arthritis Disease

Rheumatoid arthritis is a chronic autoimmune disease that is characterized by a systemic inflammatory state that affects joints and other organs .

There are many types of RA-related pulmonary diseases. RA-related pulmonary diseases include airway disease such as bronchiolitis. There are interstitial lung diseases that include non-specific interstitial pneumonitis and usual interstitial pneumonia .

The pathogenesis of RA is multifactorial with contributions from genetic and environmental factors. (CD4+) T-cells is responsible for pro-inflammatory cytokines production and subsequent joint destruction .

The aetiology of RA-ILD may be related to smoking and other factors that activate autoimmunity and the attack of post-transcriptionally modified self-proteins, such as citrullinated peptides. Citrullinated peptide can be produced in the lungs of some patients, causing a pulmonary fibrosis .

Major subtypes of RA-ILD are defined by their histopathological or (HRCT) patterns

. Programmed death-1 belongs to CD28/B7 family and is expressed on the surface of activated T cells, B cells, NK cells, dendritic cells and Treg cells. sPD-1 is the soluble form of PD-1 that is obtained by phosphoric acid hydrolysis of membrane type PD-1 .

Programmed death-1 and its ligands are important negative regulators of the immune system. .

In RA, Persistent synovial T cell activation and inflammation may be reasoned to positive regulators overexpression, aberrant expression of negative regulators or functional antagonism of these molecules by soluble factors .

sPD-1 inhibits the PD-1/PD-L signalling pathway by interacting with PD-Ls and promotes the T cell activation .