Interstitial pneumonia with autoimmune features (IPAF) Interstitial pneumonia with autoimmune features (IPAF) is a new term. The “European Respiratory Society (ERS)/American Thoracic Society (ATS) Task Force on Connective Tissue Disease-Associated Interstitial Lung Disease” was established to create terminology and classification criteria for idiopathic interstitial pneumonia with autoimmune features after research and discussion. The name of interstitial pneumonia with autoimmune features was proposed with the following diagnostic criteria: 1) the presence of interstitial pneumonia (confirmed by HRCT or lung biopsy); 2) the exclusion of other known causes; 3) the absence of a definite connective tissue disease diagnosis; 4) the presence of at least 2 of these 3 features phenomenon, etc. (2) Serological manifestations: such as antinuclear antibodies, rheumatoid factor, anti-cyclic citrullinated peptide antibodies, anti-double-stranded-DNA, anti-Ro (SSA), anti-La (SSB), anti-RNP, etc. (3) Morphological manifestations: radiologically, high-resolution CT suggested the following types: nonspecific interstitial pneumonia; mechanized pneumonia; nonspecific interstitial pneumonia overlapping mechanized pneumonia; lymphocytic interstitial pneumonia. Pathologically, lung biopsy suggests the following types: nonspecific interstitial pneumonia; mechanized pneumonia; nonspecific interstitial pneumonia overlapping mechanized pneumonia; lymphocytic interstitial pneumonia; infiltration of interstitial lymphocytes with germinal center formation; diffuse lymphoplasmacytic infiltration (with or without lymphatic follicular hyperplasia). Interpretation: In idiopathic interstitial pneumonia (IIP), it is important to identify the underlying cause from a clinical perspective, as this can affect treatment and prognosis. CTD is a group of systemic autoimmune disorders that includes rheumatoid arthritis, systemic lupus erythematosus, inflammatory myopathies, desiccation syndrome, systemic sclerosis, and mixed connective tissue diseases. Although these diseases have their unique and distinctive features, they share an underlying common mechanism – systemic autoimmunity and immune-mediated organ damage. A particularly recognizable clinical manifestation of CTD is interstitial pneumonia. Typically, interstitial pneumonia can be seen in patients with established CTD, but for some other insidious CTDs, interstitial pneumonia may also be the first or only clinical manifestation. A number of recent studies have shown that many patients diagnosed with IIP have certain clinical features that are usually not readily apparent and that suggest an underlying autoimmune process, but that are not sufficient for a diagnosis of either CTD. Others do not have typical systemic or extrathoracic manifestations but have high serum autoantibodies. In addition, imaging or histopathologic features may suggest an underlying CTD, but the lack of extrathoracic manifestations and serologic findings may limit this group of patients to a diagnosis of IIP. A new term, interstitial pneumonia with autoimmune features (IPAF), is used to describe a patient who has both interstitial lung disease and, from the clinical, serologic, and serologic morphologic features of the lungs presume the presence of a disease with an underlying systemic autoimmune condition, but does not yet meet the diagnostic criteria for CTD in rheumatic diseases. These patients are not CTDs and they are also significantly different from patients diagnosed with IIP. Finally, it is possible that some individuals initially diagnosed with IPAF may develop some sort of definite CTD over time.