Definition a group of disease which predominantly affect the pulmonary connective tissue and interstitium (between the air sacs of the lungs) of the alveolar walls and share a common response of the lung to injury: alveolitis; inflammation; fibrosis of the interalveolar septum also known as"interstitial pulmonary fibrosis or diffuse parenchymal lung disease dpld)Definition a group of disease which predominantly affect the pulmonary connective tissue and interstitium (between the air sacs of the lungs) of the alveolar walls and share a common response of the lung to injury: alveolitis; inflammation; fibrosis of the interalveolar septum  also known as―interstitial pulmonary fibrosis‖or ―diffuse parenchymal lung disease (DPLD)‖