CD69 and hypersensitivity pneumonitis: Given the increasing evidence supporting a critical role for CD69 in the retention of antigen-specific B cells and T cells in the airways, and considering that mice with abnormally low B cell numbers that strongly express CD69 appear to develop an HP-like disease in this subacute model, it may be speculated that CD69 could constitute a target of interest in the dysregulated steps leading to chronic HP.