Pathogenesis of pulmonary sarcoidosis

Changes that occur in lungs:

• events triggered by an unknown factor
• results in activation of pulmonary T cells and pulmonary alveolar macrophages
  
  
• pulmonary T cells secrete interleukin-2, resulting in:
  • increased proliferation of T helper cell clones in the lungs
  • release of monocyte chemotactic factor and attracts monocytes into the lungs, increasing the macrophage response
  • non-specific stimulation of B cells resulting in an increased production of immunoglobulins
    
    
• pulmonary alveolar macrophages release interleukin-1 and substances that enhance fibroblast chemotaxis and proliferation (e.g. fibronectin, alveolar macrophage-derived growth factor, gamma interferon):
  • release of interleukin-1, together with the expression of the HLA-DR gene on the surface of the macrophages, results in chemotaxis and proliferation of T helper cells in the lungs
  • fibroblast proliferation results in promotion of collagen synthesis and leads to eventual fibrosis

Changes that occur in the blood:

• hypergammaglobulinaemia, secondary to B cell stimulation in the lungs
• hypercalcaemia and elevated serum angiotensin-converting enzyme, secondary to activation of pulmonary alveolar macrophages
• changes that occur with respect to the T cells in the lungs is not reflected in the peripheral circulation; here, there is a lymphopenia and a reduction in the T helper/suppressor ratio