Connective tissues disorders (CTD) are a heterogeneous group of immunologically mediated inflammatory diseases. Their origins are multifactorial with genetic, constitutional and environmental elements contributing to their development. CTD refers to any disease that has the connective tissues of the body as a primary target of pathology. The connectives tissues are composed of two major structural proteins, elastin and collagen, with different types of collagen proteins in each tissue [103] . Many CTD feature abnormal immune system activity associated with inflammation. Pulmonary manifestations of CTD may include both vascular and interstitial components. From recent reports, the incidence of ILD in the context of CTD appears to be higher than previously appreciated [104, 105] . Importantly, ILD may precede the development of clinically obvious CTD, sometimes by months or years. Table 1 provides information on suggestive clinical and serological features in selected conditions. The main disorders to be considered in childhood are rheumatoid arthritis, systemic sclerosis, and systemic lupus erythematosus. The other include Sjögren syndrome, dermatomyositis and polymyositis, ankylosing spondylitis, and mixed connective tissue disease. Rheumatoid arthritis Rheumatoid arthritis (RA) is an inflammatory disorder defined by its characteristic diarthroidal joint involvement. It is the most common CTD in children, but pulmonary involvement is less frequent than in adults. Genetic and environmental factors seem to be important contributors of disease progression, with influence of sex (more frequent in male), presence of two copies of the HLA-DRB1 "shared epitope" (HLA-DR SE) and anticyclic citrullinated peptide antibody (anti-CCP), and possibly tobacco exposure [106, 107] .Almost 50% of patients with RA have specific serologic abnormalities several years before the onset of joint symptoms, and the findings of elevated serum levels of IgM rheumatoid factor or anti-CCP is associated with a high risk for the development of RA [107] . Systemic sclerosis Systemic sclerosis (SSc) is characterized by a progressive dermatologic abnormality [108] . Its etiology remains unknown; it is believed to be a complex disease in which interactions between environmental, auto-immune, and genetic factors result in various disease phenotypes [109] . Although it is a rare disease in childhood, the diagnosis is based on skin disease. Cardiopulmonary complications are common and have been associated with death in young patients. Almost all patients with SSc have serum antinuclear antibodies. The other autoantibody markers are listed in table 1. Recently, the presence of anti-DNA topoisomerase II autoantibody has been reported to be a key factor in the development of ILD, in association with class II MHC status (HLA-DR3, HLA-DPBI) [110] . Systemic lupus erythematosus Systemic lupus erythematosus (SLE) is an auto-immune disorder characterized by the involvement and dysfunction of multiple organ systems. The mechanisms of tissue injury involve autoantibody production and immunocomplex formation leading to an inflammatory process. Diverse clinical phenotypes are observed, including a variety of mucocutaneous lesions, non erosive arthropathy, renal disease (glomerulonephritis and interstitial nephritis), lung disease, pericarditis, and a spectrum of neurologic disorders. Laboratory abnormalities are characterized by the presence of antibodies reactive to nuclear (ANA) and cytoplasmic antigens.