A study published in Molecular Nutrition & Food Research(1) suggests that celery juice and celery extracts may help reduce activity by tumor necrosis factor alpha (TNF-A) and nuclear factor kappa B (NF-KB), proteins that are linked to inflammatory problems.

Another study published in Planta Medica(2) suggests that the luteolin in celery may be able to inhibit the production of COX-2, an enzyme that triggers inflammation.

All of these messaging molecules play a key role in the body's inflammatory responses, and keeping them in check is an important step in the prevention of unwanted inflammation. 

References:

Hostetler, G. et al. (2012). Flavone deglycosylation increases their anti-inflammatory activity and absorption. Molecular Nutrition & Food Research, vol. 56, no. 4, 558 – 569.

Ziyan, L., et al. (2007). Evaluation of the anti-inflammatory activity of luteolin in experimental animal models. Planta Medica, vol. 73, no. 3, 221 – 226.