TNF and inflammatory bowel disease: However, further assessment of BLEC responses by PCA performed with data pertaining parameters from BLECs treated with plasma from either healthy donors or IBD patients revealed that TNFα levels in plasma, alongside expression of claudin-5, ICAM-1 and COX-2 by BLECs, contribute reasonably evenly and on a same directional vector to the variation of the PCA mathematical model, while expression of claudin-3, VCAM-1 and ZO-1 contribute in an unrelated manner to the model, and finally, permeability to NaFlu explains very little of the variation observed (Figure 2A).