Follicular bronchiolitis consists of hyperplasia of the bronchus-associated lymphoid tissue so that airways have prominent lymphoid tissue with follicles and germinal centers. Follicular bronchiolitis can occur in collagen vascular diseases involving the lungs (particularly rheumatoid arthritis and Sjögren syndrome), in bronchiectasis, in immunodeficiency states of various types, and in hypersensitivity reactions. Some cases are idiopathic. It may also be seen in association with lymphoma of the bronchus-associated lymphoid tissue.