The
cytokine CD137, a member of the
TNF receptor family, is expressed by T cells and regulates activation and proliferation of these cells. The
CD137 ligand (CD137L) is expressed by antigen-presenting cells including macrophages, but also on various
carcinoma cells. CD137/CD137L interaction plays a central role in sustaining T cell and macrophage activation, i.e. in antitumour immunity. The present study was designed to investigate whether CD137 and CD137L
protein levels are altered in colorectal tumours compared with paired normal tissues. The CD137 and CD137L plasma levels from patients with
colorectal cancer were also examined. Collectively, we noted a significantly lower CD137L level in cancerous tissue compared with paired normal tissue, and the difference in CD137L
protein level was significantly lower in the
colon cancer subgroup compared with paired normal colon tissue. On the other hand, we found an elevated CD137
protein level in the
rectal cancer subgroup compared with paired normal rectal tissue. Patients with a tumour localised in the colon revealed significantly higher soluble CD137
protein concentration in the plasma than patients with a tumour localised in the rectum, and there was a tendency toward a higher concentration of CD137L
protein in the plasma from patients with tumour localised in the colon. Moreover, the plasma concentrations of CD137 and CD137L
proteins were strongly and significantly correlated. The different expression levels of CD137 and CD137L in the colon and rectum may reflect divergent mechanisms involved in the pathogenesis of
colorectal cancer and lead to dissimilar protective immunity.