Expression of B7 co-stimulatory molecules and CD1a antigen by alveolar macrophages in allergic bronchial asthma

Background Lung allergen recognition that takes place in the airways of ast hmatic subjects is still a controversial matter. Objective We hypothesized that a rapid allergen recognition process requires the presence, at the muc osal surface, of professional APC, such as B7(+) alveolar macrophages (AM) and/or CD1(+) dendritic cells, which usually have a lower expression in the normal human lung. Methods Studies were performed on bronchoalveolar lavag e (BAL) fluid collected from 10 untreated allergic subjects and 10 adult no rmal volunteers. Further controls consisted of five untreated pulmonary sar coidosis (PS) and four extrinsic allergic alveolitis (EAA) individuals. To ascertain whether T helper 2-type cytokines of allergen influence B7 and CD 1 antigen expression, in vitro studies were carried out using unprimed (nai ve) cord blood plastic-adherent monocytes. Results Cytofluorymetric analysi s revealed that AM from asthmatics, unlike those from normal subjects or pa tients with PS or EAA, overexpressed B7-2, CD1a and, to a lesser extent, B7 -1 surface molecules. Immunohistochemical studies confirmed the presence of CD1(+) dendritic cells in the BAL fluid from asthmatic subjects. On in vit ro cultured naive cord blood monocytes both purified Dermatophagoides ptero nyssinus allergen and T-cell cytokines, i.e. IL-4 and granulocyte macrophag e colony-stimulating factor, induced surface expression of B7-2 and CD1a re ceptors, whereas they had no appreciable effect on that of B7-1 membrane mo lecule. Conclusions Taken together, these findings support the proposal tha t airways of atopic individuals are equipped with professional APC that syn ergize with allergen-specific T cells for the recognition of intact allerge ns. When the recognition process takes place, asthmatic symptoms could deve lop in genetically susceptible individuals.