Background & aims: Lymphocyte recruitment to sites of inflammation requires the sequential engagement of adhesion molecules and chemokine receptors. In the current studies we analyzed the role of CD44 for the development of chronic small-intestinal inflammatory infiltrates in vivo.
Methods: By using a tumor necrosis factor (TNF)-driven model of chronic ileitis (ie, B6.129P-TNF(DeltaAU-rich element [ARE])) that recapitulates many features of Crohn's disease, we noticed dynamic changes in the expression and functional state of CD44 and its ligand hyaluronan via enzyme-linked immunosorbent assay, real-time reverse-transcription polymerase chain reaction, immunohistochemistry, and flow cytometry. In addition, we assessed the role of lymphocyte populations during induction of ileitis through adoptive transfer studies, and generated CD44-deficient TNFDeltaARE mice to assess the role of CD44 for development of ileitis.
Results: Soluble hyaluronan levels and expression of hyaluronan synthase-1 were increased in TNFDeltaARE mice. This coincided with increased expression of CD44 (including variant 7) and reactivity towards hyaluronan on CD4(+) T cells. CD44 was spatially colocalized with the gut-homing integrin alpha(4)beta(7), spatially linking lymphocyte rolling with arrest. These cells had an effector phenotype because they lacked L-selectin and a higher proportion in diseased mice produced TNF and interleukin-2 compared with wild-type littermates. Lastly, CD4(+) but not CD8(+) T cells conferred ileitis to RAG(-/-) recipients and deficiency of one or both alleles of the CD44 gene resulted in attenuation of the severity of ileitis in TNFDeltaARE mice.
Conclusions: Our findings support an important role of CD44 expressed by CD4(+) and CD8(+) for development of ileitis mediated by TNF overproduction.