Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immunodeficiency. Respiratory ailments are the most frequent complications of CVID, with chronic pulmonary disease developing in 30-60% and even more experiencing frequent acute respiratory infections. This project aims to establish cutting-edge approaches to study pulmonary biology in CVID and apply novel bioinformatics strategies to study complex interactions among microbes and host cells by direct sampling of the respiratory tract. The central hypothesis for this research is that antibody (Ab) deficiency in CVID alters respiratory microbiota and host interactions to drive pulmonary disease.