Lymphocytic Interstitial Pneumonia (Lymphoid Interstitial Pneumonitis) By Joyce Lee, MD, MAS, University of Colorado School of Medicine Reviewed / Revised Jun 2021 | Modified Sep 2022 View Patient Education Symptoms and Signs Diagnosis Prognosis Treatment Key Points Topic Resources Lymphocytic Interstitial... Lymphocytic interstitial pneumonia (LIP) is lymphocytic infiltration of the alveolar interstitium and air spaces.