Systemic autoimmune diseases (SAD) are a heterogeneous group of immunologically mediated inflammatory disorders including multiorgan involvement. As expected in a multisystem disease, the entire pulmonary system is vulnerable to injury. Any of its compartments may be independently or simultaneously affected. It is difficult to assess the true prevalence of lung disease in cases of SAD. In this article, we will review the pulmonary manifestations caused by systemic lupus erithematosus, rheumatoid arthritis, systemic sclerosis, polymyositis/dermatomyositis, Sjögren’s syndrome, mixed connective tissue disease, Wegener’s granulomatosis, Churg-Strauss syndrome, Goodpasture’s syndrome, and ankylosing spondylitis.
Immunologic lung diseases develop when the normal mechanisms of immune self-tolerance fail. Macrophages and lymphocytes are the key cells involved in the initiation and perpetuation of the acquired immune response in the lung. Macrophages serve as scavenger cells, ingesting and degrading the inhaled antigenic load. In addition, these cells serve as antigen-presenting cells for T lymphocytes. Relatively few lymphocytes are present in the normal lung parenchyma. However, after stimulation by the relevant antigen in the surrounding lymphoid tissues, lymphocytes specific for that antigen migrate to the lung and participate in the inflammatory response. Essentially all SAD appear to be dependent on the inappropriate activation of autoreactive CD4 T cells as well as autoreactive B cells responsible for the pathogenic autoantibodies. Depending on the underlying autoimmune process, the pleura, pulmonary parenchyma, or airway may be predominantly affected. SAD are a heterogeneous group of diseases, which frequently involve the lungs. The pleuropulmonary manifestations of these diseases are diverse, affecting all anatomic locations of the respiratory tract (i.e. airways, alveoli, blood vessels, and pleura). Although pulmonary complications generally occur in patients with well established disease occasionally the lung involvement is the first manifestations of the autoimmune disorder. Further studies are therefore needed to better understand these conditions, and to develop more effective rational therapies