Regulation of B-cell-activating factor expression on the basophil membrane of allergic patients.

Background: To investigate the modulation of B-cell-activating factor (BAFF) expression on the basophil membrane of allergic patients. BAFF is an important regulator of B-cell activation, proliferation and immunoglobulin production, which may play a role in respiratory allergic diseases in promoting the production of IgE by B cells.

Methods: Peripheral blood samples of 10 patients with allergic rhinitis, 3 with severe asthma and fungal sensitization (SAFS), 3 with allergic bronchopulmonary aspergillosis (ABPA) and 11 healthy controls were assessed regarding BAFF (CD257) expression using the basophil activation test before and after stimulation with IgE and allergens, as well IgE-independent stimuli, like fMLP, lipotheichoic acid from Staphylococcus aureus (LTA-SA) and lipopolysaccharide (LPS).

Results: BAFF membrane expression did not change after IgE and allergen stimulation both in patients and controls, while it was upregulated by Aspergillus stimulation, both in sensitized patients and controls. In both patients and controls, BAFF expression was significantly upregulated following LTA-SA and β-1,3-glucan exposure (toll-like receptor-2 ligands), but not following LPS stimulation.

Conclusions: Basophils from allergic and healthy subjects constitutively express membrane BAFF, which is not upregulated by IgE or specific allergens but by TLR-2 ligands (LTA-SA and β-1,3-glucan). Aspergillus fumigatus stimulation was able to upregulate BAFF expression on the basophils of sensitized asthmatic patients, but not via IgE-dependent mechanisms, since results did not differ between the patient and control groups. These findings suggest that basophils may contribute to the polyclonal production of IgE commonly observed in patients with SAFS and ABPA.