CD49d+ neutrophils produce a soluble factor that induces expression of the high affinity IgE receptor (FcεRI) on murine lung dendritic cells

RATIONALE: Development of childhood asthma is strongly associated with respiratory viral infections. With the Sendai virus (SeV) mouse model we demonstrated expression of the high affinity IgE receptor, FcεRI, on murine lung conventional dendritic cells (cDC) was required for post-viral airway disease. Expression of cDC FcεRI partially depends on cognate interactions between cDC and CD49d expressing neutrophils (CD49d⁺PMN). PMN that do not express CD49d (CD49d^–PMN) are unable to induce cDC FcεRI expression. It remains possible that CD49d⁺PMN produce a soluble factor that coupled with CD49d^–PMN induces cDC FcεRI expression.

METHODS: cDC were isolated from naïve C57BL6 mice by immunomagnetic selection. BAL CD49d⁺ and CD49d^–PMN were isolated 3 days post SeV inoculation using flow sorting. CD49d⁺PMN were cultured in complete RPMI-10 for 48 hours and supernatant collected. Using a SpeedVac, supernatant was concentrated 2 fold. CD49d­­^–PMN and cDC were co-cultured with increasing CD49d⁺PMN supernatant concentrations. After 48 hours, cDC FcεRI expression was measured by flow cytometry. Data are presented as net MFI from IgG control.

RESULTS: Un-concentrated CD49d⁺PMN supernatant led to a net MFI expression of FcεRI on cDC of 95.0 (n=1). Co-culturing cDC with 2 fold concentrated CD49d⁺PMN supernatant led to a net MFI of 276.5±41.5 (mean±SEM, n=2), demonstrating a direct relationship between FcεRI expression and CD49d⁺PMN supernatant.

CONCLUSIONS: CD49d⁺PMN appear to express a soluble factor that induces expression of cDC FcεRI in a dose dependent fashion, when cultured with CD49d^–PMN. Further studies will be aimed at identifying this soluble factor, and developing strategies to inhibit it therapeutically.