Changes in lung macrophages during disease.

The alveolar macrophage pool is morphologically and phenotypically heterogeneous. Using monoclonal antibodies, homogeneous populations were isolated from broncho-alveolar lavage for functional studies. Such investigations revealed that some alveolar macrophages exhibit phagocytic and microbicidal capacity, thus being equipped to act as effector cells (MoAb RFD7+), while others exhibit the characteristics of antigen presenting cells (MoAb RFD1+) involved in the induction of acquired T cell responses. In the investigation of cells from sarcoid patients, a third population was revealed, exhibiting the phenotype RFD1+ and RFD7+. Functional studies of such cells showed them to act by suppressing T-cell responsiveness. The balance between these three populations alters in different disease processes and, in the case of sarcoidosis, is related to disease severity. It is proposed that changes in the balance of these populations may directly influence the pathogenesis of inflammatory lung disease.