Combination of bronchial asthma (BA) and gastroesophageal reflux disease (GERD) is a widespread clinical situation. The two pathologies are known to influence each other leading to disturbances in immune responsiveness. We studied phenotypes and phenotypic plasticity of immune cells (alveolar macrophages) in patients with BA and GERD. It was shown that BA and GERD are largely associated with AM of proinflammatory M2 and anti-inflammatory M1 phenotypes respectively. Population of AM with MI phenotype increases in patients having both BA and GERD compared with that in BA alone. In vitro experiments showed that acidic milieu promotes shifting the phenotype toward the predominance of M1, i.e. simulates the situation characteristic of GERD. Combination of BA and GERD narrows the interval within which AM can change MI phenotype (i.e. makes them more "rigid") but broadens the range in which they can change M2 phenotype. Also, GERD promotes the development of morphological rigidity of AM. Patients with BA given steroid therapy undergo inversion of phenotypic plasticity of AM. These data characterize the immunological component of BA and/or GERD pathogenesis. They help to better understand mechanisms of development of broncho-pulmonary pathology in GERD patients and can be used to work out new methods for the treatment of these diseases.