Lymphocyte ectoenzyme activity compared in healthy persons and patients seropositive to or at high risk of HIV infection

Celebrating 100 years of Immunology & Cell Biology - a special focus on the field of tumor immunology in Australia

In this Commentary article, as part of the 100-year celebrations of the journal, we reflect on the contribution of articles published in ICB in the field of tumor immunology. A highlight is a series of interviews conducted with three Australian-based ICB authors who have contributed key papers over the years: Rajiv Khanna, Delia Nelson and Ian Frazer.

The 5'-nucleotidases as regulators of nucleotide and drug metabolism

The 5'-nucleotidases are a family of enzymes that catalyze the dephosphorylation of nucleoside monophosphates and regulate cellular nucleotide and nucleoside levels. While the nucleoside kinases responsible for the initial phosphorylation of salvaged nucleosides have been well studied, many of the catabolic nucleotidases have only recently been cloned and characterized. Aside from maintaining balanced ribo- and deoxyribonucleotide pools, substrate cycles that are formed with kinase and nucleotidase activities are also likely to regulate the activation of nucleoside analogues, a class of anticancer and antiviral agents that rely on the nucleoside kinases for phosphorylation to their active forms. Both clinical and in vitro studies suggest that an increase in nucleotidase activity can inhibit nucleoside analogue activation and result in drug resistance. The physiological role of the 5'-nucleotidases will be covered in this review, as will the evidence that these enzymes can mediate resistance to nucleoside analogues.

CD26: a multifunctional integral membrane and secreted protein of activated lymphocytes

CD26 has proved interesting in the fields of immunology, endocrinology, cancer biology and nutrition owing to its ubiquitous and unusual enzyme activity. This dipeptidyl aminopeptidase (DPP IV) activity generally inactivates but sometimes alters or enhances the biological activities of its peptide substrates, which include several chemokines. CD26 costimulates both the CD3 and the CD2 dependent T-cell activation and tyrosine phosphorylation of TCR/CD3 signal transduction pathway proteins. CD26 in vivo has integral membrane protein and soluble forms. Soluble CD26 is at significant levels in serum, these levels alter in many diseases and soluble CD26 can modulate in vitro T-cell proliferation. CD26, being an adenosine deaminase binding protein (ADAbp), functions as a receptor for ADA on lymphocytes. The focus of this review is the structure and function of CD26 and the influence of its ligand binding activity on T-cell proliferation and the T cell costimulatory activity of CD26.

Lymphocyte 5'-ectonucleotidase: an indicator of oxidative stress in humans?

Lymphocytic 5'-ectonucleotidase (NT) activity previously has been shown to be reduced in patients with a high pro-oxidant state. This study shows that NT activity is decreased in vitro by exposure to superoxide anions and that ascorbate protects against this effect. Also, a putative high pro-oxidant state in vivo, as indicated by low tissue ascorbate levels, resulted in a significant decrease in NT which an antioxidant intake normalized. These results taken together suggest that NT is sensitive to superoxide anion and that it may be a good marker of a pro-oxidant state in humans.

Successful immunomodulating in AIDS patients with ursodeoxycholic acid--a pilot study

Based on the positive therapeutic results with ursodeoxycholic acid (UDCA) in patients with primary biliary cirrhosis, in whom we observed a clinical improvement in conjunction with the normalization of the low pretreatment dipeptidyl peptidase (DPIV, CD26) expression of peripheral blood lymphocytes (PBL), we hypothesized that the very low DPIV expression in AIDS patients could be positively influenced by UDCA. Four young male AIDS patients were therefore treated with 750 mg of UDCA for 4 months. The low CD26 expression (2-8% of the PBL versus 18-28% in healthy controls) at the beginning of the study rose to 10-16% after UDCA therapy. Simultaneously we observed a two-to-three-fold elevation of the absolute number of lymphocytes as well as a slight increase of CD4+ cells. These effects were similar in all examined patients. Further investigations should be conducted on this potentially beneficial effect of UDCA.

A semi-automated method for 5'-ectonucleotidase measurement in lymphocytes

We describe a simple, non-radioactive, semi-automated method for measuring lymphocyte ecto-5'-nucleotidase activity in isolated cell homogenates. The method which uses inosine 5'-monophosphate (IMP) as a substrate was optimized and requires a total of 4 x 10(6) lymphocytes. The reference range obtained (38.7-180.0 nmol/h per mg protein; means = 106.6) agrees with other isotopic methods which use 14C-IMP. The simplicity, sensitivity (lower limit 10, upper limit 400 nmol/h per mL) and precision (at 114 nmol/h per mL, interday 4.2% s.d., n = 20; intraday 5.8%, n = 10) makes this method suitable for routine clinical laboratory use.