Interleukin-12 p40 m-RNA expression in human kidney allograft biopsies

Interleukin-12 (IL-12) is a heterodimeric cytokine implicated in the early differentiation of naive T-lymphocytes into the Th1 subset. IL-12 is important for induction of the cellular immune response against viruses, intracellular parasites and neoplasms. Its role in alloresponsiveness has not been fully elucidated. Preliminary data in the literature point toward the prevalence of Th1 lymphocytes in processes of allograft rejection. In attempt to further investigate the expression of this cytokine during episodes of cellular rejection of renal allografts, we searched for IL-12 message in human kidney allograft biopsies using the reverse transcriptase-polymerase chain reaction technique. Twenty-three allograft core biopsies from 19 patients were obtained percutaneously for clinical indications in 18 cases, and as part of an investigational protocol in five cases. A portion of the tissue was used for RNA extraction using the guanidium-thiocyanide phenol-chloroform method. Histology was performed on the remaining core material. Ten mg of total RNA were used for reverse transcription. PCR of the c-DNAs was done for 40 cycles using primers for the p40 subunit of IL-12 and GAPDH which was used as a control. PCR products were photographed after electrophoresis, transferred to a nylon membrane and hybridized with a radiolabelled cloned human IL-12 p40 1 kb c-DNA fragment. Autoradiographies were developed after 20-min exposure. All samples were run in triplicate. IL-12 p40 m-RNA was expressed in all 17 biopsies showing acute cellular rejection as well as in all three biopsies showing focal interstitial fibrosis. No message was found in the presence of normal allograft histology. This is the first in vivo report of IL-12 p40 subunit m-RNA expression during renal allograft rejection in humans. The role of this Th1 cytokine in the alloresponse deserves further investigation.