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P337 Anti-TNFalpha therapy is associated with rapid reduction of circulating monocyte numbers and blunted monocyte pro-inflammatory response in patients with Crohn’s disease

S. Slevin*1, C. Dennedy2, A. Ribeiro1, R. Ceredig1, M. Griffin1, L. Egan2

1National University of Ireland Galway, REMEDI, Galway, Ireland, 2National University of Ireland Galway, Pharmacology and Therapeutics, Galway, Ireland

Background

Monocytes, recently classified as CD14++/CD16- (classical), CD14++/CD16+ (intermediate), and CD14+/CD16++ (non-classical) are considered to play a role in the pathogenesis of Crohn’s disease (CD) and may be a specific target of anti-TNFalpha therapies. We studied the acute effects of the anti-TNFalpha monoclonal antibody (mAb) infliximab (IFX) on blood monocytes and their subsets in a cohort of CD patients.

Methods

We conducted multi-colour flow cytometry of freshly-isolated peripheral blood mononuclear cells from healthy adults (Ctrl, n = 21) and adults with CD (n = 32) before (CD Trough-IFX) and immediately following (CD Peak-IFX) IFX infusion, and then monocyte apoptosis (cleaved caspase 3) and LPS-stimulated TNF and IL-12 production by intracellular staining of CD Trough-IFX and CD Peak-IFX samples.

Results

The mean total blood monocyte count was strikingly reduced from 10.6 ± 9.5 to 4.6 ± 4.4 x 104/ml following IFX infusion in CD patients (p < 0.0001). All monocyte subsets were reduced in number following IFX in the CD cohort but the magnitude of reduction was greater for classical (trough vs peak; 7.5 ± 6.3 and 3.4 ± 3.4 x104/ml, p < 0.0001) and intermediate (trough vs peak; 3.5 ± 2.7 and 1.9 ± 1.9 x104/ml, p < 0.0001) compared with non-classical (trough vs peak; 9.9 ± 6.8 and 7.1 ± 6.0 x103/ml, p = 0.01). Monocyte apoptosis (% cleaved caspase 3+) was low in CD Trough-IFX samples (0.6 ± 0.6%) and was not increased in CD Peak-IFX samples (0.4 ± 0.3%). Following ex vivo LPS stimulation, the average percent of monocytes expressing intracellular TNF+ was significantly lower in CD Peak-IFX samples at 65.2% than in CD Trough-IFX samples, 89.5%. Similar results were also obtained for intracellular IL-12+ expression (Peak-IFX 36.8% and Trough-IFX 55.9%).

Conclusion

IFX infusion is associated with a striking reduction in circulating monocytes in CD patients with the greatest effect on classical and intermediate subsets. This is not associated with induction of apoptosis but is accompanied by blunting of monocyte pro-inflammatory response to TLR4 ligation.