The presence of interleukin-2 receptor alpha in the serum of colorectal cancer patients is unlikely to result only from T cell up-regulation.

It is unclear whether the presence of interleukin-2 soluble receptor alpha (IL-2 sRα) in the serum of colorectal cancer patients is solely due to T cell activation. In this study, we therefore investigated whether T cell activation, indicated by the up-regulation of the CD25 and HLA-DR markers, or cell-mediated immunity (CMI) were associated with increased serum levels of IL-2 sRα in patients with advanced colorectal carcinoma. The levels of serum IL-2 sRα and the proportion of T cells expressing HLA-DR (DR⁺ T cells) were measured as markers for chronic activation. CMI was assessed by delayed-type hypersensitivity reaction (DTH) to intradermal injections of recall antigens. Eighty-seven colorectal liver metastases (CLM) patients and 23 'cancer-free' control subjects were studied. DR⁺ T cells were found to be more prevalent (P<0.0001) in CLM patients (median: 21.1%) than in controls (median: 3.4%), but DR⁺ T cell up-regulation was not correlated with serum IL-2 sRα levels. CMI positivity was significantly reduced (P=0.002) in CLM patients compared with controls, and this reduction was significantly associated (P=0.05) with an increase in the number of DR⁺ T cells. Although survival was significantly shorter (P=0.0003) in patients with increased serum IL-2 sRα levels than in subjects with normal levels, no association was found between survival and DR⁺ T cell up-regulation. These findings were consistent with the hypothesis of an additional source of serum IL-2 sRα other than T cell up-regulation in CLM patients – either from other immune cells, or from tumour products. [ABSTRACT FROM AUTHOR]