We have described recently that TNBS-induced colitis, an animal model of chronic inflammatory bowel disease (IBD), can be cured by treatment with anti-CD44v7. This finding led us to evaluate whether CD44v7 may be of functional importance in patients with IBD. Expression of CD44 variant isoforms (CD44v) has been evaluated on PBMC of 46 patients with IBD, 43 patients with autoimmune diseases not affecting the gastrointestinal tract, 26 patients with nonautoimmune disease, and 24 healthy donors. In all groups, expression of CD44v on freshly harvested PBMC was not above or was borderline above background levels. After in vitro stimulation, expression of CD44 standard (CD44s) and CD44v6 was strongly up-regulated. Exclusively on PBMC of patients with autoimmune disease, high expression of CD44v3 and CD44v7 was observed. CD44v3 and CD44v7 were mainly expressed on subsets of CD4+ lymphocytes, B cells, and monocytes; CD44v6 was predominantly detected on CD4+ and CD8+ cells. Considering functional activity, CD44v7 apparently exerted a dual effect. After culturing PBMC in the presence of anti-CD44v7, a higher percentage of cells produced IL-10. This was irrespective of whether the PBMC were derived from healthy donors or from patients with autoimmune disease or IBD. On the other hand, PBMC of all donors proliferated upon cross-linking of CD3 and CD44s or CD3 and CD44v6. Instead, costimulatory activity of CD44v7 was seen only in PBMC of patients with autoimmune disease and IBD. Because expression and function of CD44v7 in patients with systemic autoimmune disease and IBD have been much like the ones in mice suffering of TNBS-induced colitis, it is tempting to speculate that blockade of CD44v7 could also be of therapeutic relevance in the human diseases.