Heparan Sulfate-Bound Dimeric IL-2: A Potential Mediator of Renal Ischemic Injury.

Abstract

Interleukin-2 (IL-2) is a multifaceted cytokine that exhibits immunostimulatory and immunosuppressive properties. While primarily known as a monomer, a dimeric form of IL-2 has been identified in fish optic neurons, and this dimeric form was reported to be toxic to oligodendrocytes. Given this observation, we asked whether dimeric IL-2 is found in mammalian tissues. To this end, murine and human aorta and kidney tissues were homogenized and assessed by Western blot analysis for the presence of IL-2. Dimeric (30 kD) IL-2 was identified in each tissue. To determine whether dimeric IL-2 is retained by heparan sulfate, we digested the tissues with heparinase. Dimeric IL-2 was liberated, suggesting that dimeric IL-2 is bound, at least in part, by heparan sulfate. To ascertain whether dimeric IL-2 in murine or human tissues is cytotoxic, we treated cultures of renal tubular epithelial cells with increasing concentrations of dimeric IL-2 that was purified by electroelution from zinc-stained preparatory gels. Signs of cytotoxicity, including membrane blebbing and lactate dehydrogenase release, were apparent within 15 minutes of dimer addition. Commercial IL-2, isolated in an identical fashion to dimeric IL-2, was not cytotoxic. Systemic administration to mice of 10 ug of dimeric IL-2 induced vacuolization of renal tubular epithelium, a morphology typically seen with ischemic injury. Finally, murine kidneys subjected to 60 minutes of ischemia, as compared to sham controls, expressed greatly increased amounts of dimeric IL-2 in both tissue homogenates and heparinase digests. These results suggest that dimeric IL-2 may contribute to acute tubular necrosis and, in turn, renal dysfunction, induced as a consequence of severe hypotension, dehydration, sepsis, or reperfusion injury.