Overexpression of the human 2-oxoglutarate carrier lowers mitochondrial membrane potential in HEK-293 cells: contrast with the unique cold-induced mitochondrial carrier CGI-69.

Using differential mRNA expression analysis, a previously uncharacterized gene was found to be up-regulated 2-fold in brown adipose tissue (BAT) of mice exposed to cold (4 degrees C) for 48 h. Contig and homology analysis revealed that the gene represents the murine orthologue to a sequence from a public database encoding a putative human protein (CGI-69). The presence of mitochondrial carrier domains in the human protein, its transmembrane topology and cold-induction of the mouse CGI-69 gene in BAT prompted an analysis of the idea that CGI-69 may represent a new uncoupling protein (UCP) functional homologue. However, transfection of human CGI-69 isoforms in HEK-293 cells yielded no change in mitochondrial membrane potential (Deltapsi(m)), despite localization of FLAG-tagged CGI-69 to mitochondria of MCF7 cells. Surprisingly, overexpression of the human 2-oxoglutarate carrier (OGC) protein (originally designed as a negative control) sparked a significant drop in Deltapsi(m), possibly signalling a previously unappreciated uncoupling activity for the OGC.

Differential responses to interleukin 2 define functionally distinct subsets of human natural killer cells.

Human natural killer (NK) cells can be subdivided into two populations based on the density of cell surface CD56 antigen. The great majority (approximately 90%) of NK cells express CD56 at low levels (the CD56dim phenotype), whereas a small NK cell subset (approximately 10%) exhibits approximately fivefold greater density of surface CD56. Exposure to exogenous interleukin 2 (IL 2) induces tenfold greater proliferation of CD56bright cells compared to CD56dim lymphocytes, even though both subsets constitutively express similar levels of intermediate affinity IL 2 receptor (IL 2R) p75 chains. Incubation with IL 2 alone or irradiated target cells alone could induce expression of the IL 2R p55 chain by both CD56bright and CD56dim NK cells; a combination of both stimuli was most effective. IL 2R p55 induction was evident after co-culture of NK cells with both NK-sensitive and NK-resistant cell lines or with antibody-coated target cells. Activation of NK cells with IL 2 plus target cells resulted in enhanced proliferation compared to activation with IL 2 alone; target cells alone did not induce significant proliferation. Although both NK cell subsets appeared to express high-affinity IL 2R p75/p55 heterodimers after stimulation with target cells and IL 2, proliferation of CD56dim cells remained minimal after such activation; activated CD56dim cells consistently demonstrated less proliferation to IL 2 than did resting CD56bright cells. In contrast, CD56bright NK cells exhibited even greater proliferation after stimulation with target cells. Almost all CD56dim NK cells expressed CD16 (Fc gamma R III) as well as the NK zeta chain, whereas less than 50% of CD56bright cells express either CD16 or zeta. CD56bright and CD56dim lymphocytes, thus, appear to represent distinct subpopulations of NK cells with different functional activities. Unlike CD56bright cells, CD56dim NK cells do not proliferate optimally to IL 2, even after the latter have been stimulated to express both IL 2R p55 and IL 2R p75. Efficient proliferation of CD56dim NK cells may, thus, require additional or alternative signals.

Clinical and immunologic effects of prolonged infusion of low-dose recombinant interleukin-2 after autologous and T-cell-depleted allogeneic bone marrow transplantation.

Bone marrow transplantation (BMT) can produce prolonged clinical remission in some patients with hematologic malignancies. Unfortunately, disease relapse may occur despite BMT. Studies in animal models and clinical experience have provided evidence that immunologic factors play an important role in preventing relapse post-BMT. To stimulate immunologic activity in patients post-BMT, we administered prolonged uninterrupted continuous infusions of low-dose recombinant interleukin-2 (rIL-2). Thirteen marrow recipients (seven autologous BMT, six CD6 T-depleted allogeneic BMT) received rIL-2 at a dose of 2 x 10(5) U/m2/d for a scheduled period of 90 days. rIL-2 was administered through a Hickman catheter with a portable pump beginning a median of 85 days after BMT. Toxicity was minimal and all treatment could be undertaken in the outpatient setting. No patient developed any signs of graft-versus-host disease, hypotension, or pulmonary capillary leak syndrome. Treatment did not affect the absolute neutrophil count or hemoglobin level, but eosinophils increased substantially in most patients. Platelet counts decreased by 20% in 10 of 13 individuals within 2 weeks, but stabilized thereafter. Despite the low dose of rIL-2 administered, significant immunologic changes were noted. Specifically, all 13 patients experienced a marked increase (fivefold to 40-fold) in natural killer (NK) cell number. Phenotypic characterization showed that the majority of NK cells were CD56bright+ CD16+ CD3-. In contrast, a minor increase in T-cell number was noted in only 4 of 13 patients. Low-dose rIL-2 treatment resulted in augmentation of in vitro cytotoxicity against K562 and COLO tumor targets. This cytotoxic activity could be dramatically enhanced by incubation with additional rIL-2 in vitro. The immunologic effects of rIL-2 treatment were similar in both autologous and allogeneic marrow recipients. Our data suggest that prolonged infusion of rIL-2 at low doses is safe and can selectively increase NK cell number and activity after BMT. Further studies to assess the impact these changes may have on disease relapse post-BMT will be undertaken.