Background/Purpose: Deficiency of the IKK-related kinases IKKε synergizes with the anti-inflammatory effects of IFNß in a murine model of arthritis., and this effect is mediated by IL-1Ra. To further explore the relationship between IFN signaling and IKKε, IKKε null mice were intercrossed with IL1Ra or type I interferon receptor deficient mice and evaluated in the passive K/BxN model of arthritis. 

Methods:

IKKε null, Il1rn (which encodes IL-1Ra) null, IL1Ra/IKKε null, IFNAR1 null, IFNAR1/IKKε null and wild type mice were injected with 150 ul of pooled K/BxN sera on day 0. Clinical response and histologic scores were assessed. Gene expression was measured by quantitative PCR. Mice were injected intraperitoneally with thioglycollate. The peritoneal lavage was evaluated for cell counts. The number and viability of neutrophils was determined by flow cytometry. Gene expression and protein production were tested by qPCR and western blot respectively.

Results:

IKKε null mice had a modestly attenuated course of arthritis (area under the curve [AUC] for ankle diameter=5.1 vs. 5.9 for wild type controls, P<0.05). In contrast IFNAR1 null mice (AUC 6.3 vs. 5.9, P<0.05) and Il1rn^-/- mice (AUC 11.4 vs. 5.9 P<0.01) had more severe serum transfer arthritis than wild type mice. The IL1Ra/IKKε null had arthritis similar (AUC 12.1) to the Il1rn^-/- mice (AUC 11.4). Unexpectedly, IFNAR1/IKKε null mice (AUC 7.9, P<0.05) had even greater disease severity than the IFNAR1 null (AUC 6.3) mice. The ankle histology scores in each strain correlated well with the clinical course. Of interest, quantitative PCR of arthritis paws showed a significant increase in the neutrophil chemotactic protein GCP2 in the IFNAR1 (98+10) and IFNAR1/IKKε (81+11) null compared to the WT (19+1) mice (p<0.05).  There was no difference in IL-6, IL-1ß, IL-1a or IFNb in the IL1Ra/IKKε null or IFNAR1/IKKε null mice compared to the individual knockout controls. Concordant with higher GCP2 expression mice deficient in IFN signaling recruited higher numbers of neutrophils into the peritoneum after thioglycollate challenge: 4.6+1 (WT), 6.1+2 (IKKε), 15.8+4.8 (IFNAR1) and 13.5+2.8 (IFNAR1/IKKe) x10⁶ neutrophils (p<0.05).  The neutrophils recovered from the IFNAR1/IKKε mice, however, expressed higher mRNA and protein levels of the anti-apoptotic protein Mcl1 than those of the individual knockout controls, suggesting that the deficient neutrophils had defective apoptosis.

Conclusion:

IKKε deficiency did not offset increased severity in IL-1Ra deficiency supporting a direct role of IL-1Ra in reducing arthritis. Surprisingly, IKKε deficiency increased disease severity in the IFNAR null mice, most likely due to increased neutrophil recruitment and prolonged survival.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ikk%ce%b5-deficiency-prolongs-neutrophil-survival-paradoxically-prolonging-inflammation-in-the-absence-of-a-type-i-interferon-response/