Light micrograph section through human lung tissue showing non-specific interstitial pneumonia (NSIP). This is a rare disorder that affects the tissue that surrounds and separates the tiny air sacs of the lungs. These air sacs called the alveoli, are when the exchange of oxygen and carbon dioxide takes place between the lungs and bloodstream. With interstitial pneumonia, the mesh-like walls of the alveoli become inflamed. Over time, this inflammation can lead to permanent scarring of the lungs.