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P094. Defective CSF2RB signaling in Crohn's disease patients bearing the NCF4 risk allele

R. Somasundaram1, C.J. van der Woude1, M. Peppelenbosch1, G. Fuhler1, 1Erasmus mc, Gastroenterology and Hepatology, Rotterdam, Netherlands

Background

At least 100 risk loci associated with Crohn's disease (CD) have been identified, many of which are associated with innate immunity. One of the single nucleotide polymorphisms shown to confer risk of CD development is a T to C conversion in the NADPH oxidase gene NCF4 (rs4821544). This protein plays a pivotal role in the production of reactive oxygen species (ROS) by granulocytes (PMN), essential for bactericical activity. We previously showed that GMCSF primed ROS production is impaired in rs4821544 carrying CD patients. Interestingly, the GMCSF-receptorβ gene (CSF2RB) lies adjacent to the NCF4 gene. Here, we assessed CSF2RB function between CD patients bearing the NCF4 risk and wildtype alleles.

Methods

PMN were freshly isolated from risk allele rs4821544 and wild type allele carrying patients, simultaneously. Expression of CSF2RB was determined by flowcytometry and confirmed by qPCR. ROS production upon stimulation of cells with fMLP with or without prior priming with GMCSF or GCSF was measured by flowcytometry. Uptake and killing of E. coli were measured using fluorescence spectophotometry. CSF2RB signaling was studied after stimulation with GMCSF and IL5.

Results

Membrane expression of CSF2RB is similar between patients bearing either T or C alleles. GMCSF-primed ROS production was greatly diminished in C allele patients compared to T allele patients (n = 10, 221±41 MFI vs 464±52 MFI, p = 0.002), wereas GCSF-primed ROS production was unaffected (p = 0.79) indicating a specific GMCSF receptor signaling defect. E. coli uptake was not different, whereas a trend towards diminished killing was observed in C allele patients. In C-allele patients, GMCSF stimulation induced less activation of STAT3 (n = 5, 1.8±0.8 vs 3.5±1.1 vs); AKT (11±5 vs 23±13) and ERK (30±20 vs 40±10) in C allele carriers. IL5 induced lower STAT5 (n = 4, 0.2±0.1 vs 0.5±0.2) and AKT signaling (0.03±0.06 vs 0.7±0.04).

Conclusion

We show a specific defect in CSFR2B signaling in patients carrying the NCF4 risk allele. The CSFR2B receptor is used by both GMCSF and IL5, and both cytokines induce reduced signaling in C-allele patients. In contrast, priming of PMN by GCSF, which signals through a different receptor, was normal. Thus, the NCF4 risk allele confers a defect in CSFR2B signaling, and may identify a subset of CD patients whose inflammation is influenced by impaired innate immunity induced by neutrophils. GM-CSF treatment, which is beneficial for some patients, may be limited by NCF4 genetic background of patients.