Antigen trafficking and accessory cell function in respiratory epithelial cells

We investigated accessory cell function, antigen (Ag) trafficking, and upta ke of immune complexes in isolated nasal epithelial cells (NEC) and airway epithelial cells (AEC), as well as in the two respiratory epithelial cell l ines A549 and BEAS-2B. The NEC and AEC were capable of supporting Ag-specif ic as well as phytohemagglutinin-induced and anti-CD3 antibody-induced T-ce ll proliferation. We colocalized fluorescein isothiocyanate (FITC)-labeled Ags with human leukocyte antigen (HLA)-DR in A549 and BEAS-2B, utilizing la ser confocal microscopy. Respiratory epithelial cells stimulated and unstim ulated with interferon (IFN)-gamma were pulsed with FITC-labeled Ags for va rying periods and evaluated for their ability to internalize Ag. In the uns timulated cells, intracellular punctate staining was evident at 60 min and persisted up to 120 min. In the IFN-gamma-stimulated cells (100 U/ml for 48 h), uptake occurred at 30 min, was maximal at 60 min, and diminished at 12 0 min. We conducted kinetic studies in the A549 and BEAS-2B cells, utilizin g electron microscopy with colloidal gold-conjugated Ags (Au-OVA). At 15 mi n, Au-OVA was evident in the early compartments resembling the compartment of uncoupling of receptor and ligand. At 30 min, multivesicular bodies were labeled with Au-OVA, and by 60 min Au-OVA was present in the primary and s econdary lysosomes. The FITC-labeled Ags colocalized with an early endosoma l marker (anti-cathepsin D), a late endosomal marker (M6PR), a lysosomal ma rker (CD63), and with 3-(2,4-dinitroanilino)-3 '-aminomethyldipropylamine, a marker of acidic vesicles. The BEAS-2B and A549 cells, and NEC and AEC, e xpressed surface Fe gamma receptor and internalized IgG immune complexes. T he NEC and AEC also expressed the costimulatory molecules CD80 and CD86 as determined with flow cytometry, the reverse transcription-polymerase chain reaction for RNA, and immunohistochemistry, and T-cell proliferation could be blocked by treating NEC and AEC with anti-CD80 and anti-CD86 antibodies. Our findings suggest that respiratory epithelial cells may have a role in local Ag presentation.