Direct assessment of the role of NK cells in autoimmune diabetes

Targeting natural killer cell reactivity by employing antibody to NKp46: implications for type 1 diabetes

Natural killer (NK) cells belong to the innate lymphoid cells. Their cytotoxic activity is regulated by the delicate balance between activating and inhibitory signals. NKp46 is a member of the primary activating receptors of NK cells. We previously reported that the NKp46 receptor is involved in the development of type 1 diabetes (T1D). Subsequently, we hypothesized that blocking this receptor could prevent or hinder disease development. To address this goal, we developed monoclonal antibodies for murine NKp46. One mAb, named NCR1.15, recognizes the mouse homologue protein of NKp46, named Ncr1, and was able to down-regulate the surface expression of NKp46 on primary murine NK cells following antibody injection in vivo. Additionally, NCR1.15 treatments were able to down-regulate cytotoxic activity mediated by NKp46, but not by other NK receptors. To test our primary assumption, we examined T1D development in two models, non-obese diabetic mice and low-dose streptozotocin. Our results show a significantly lower incidence of diabetic mice in the NCR1.15-treated group compared to control groups. This study directly demonstrates the involvement of NKp46 in T1D development and suggests a novel treatment strategy for early insulitis.

Immunological effects of a hyperinsulinaemic euglycaemic insulin clamp in healthy males

The purpose of this study was to determine the in-vivo and in-vitro effects of insulin, at physiological and supraphysiological concentrations, on the human immune system. Ten healthy young men went through a sequential two-step hyperinsulinaemic euglycaemic clamp. Plasma insulin concentrations were increased from baseline (9.0 microU/ml) to 49.1 microU/ml after 1 h of insulin infusion (step I) and to 1281 microU/ml (step II) after 2 h of infusion. As control experiments infusions of isotonic saline were performed. The unstimulated natural killer (NK) cell activity among blood mononuclear cells (BMNC) increased in response to supraphysiological plasma insulin levels (baseline versus step II: 20.6 +/- 11.3 versus 27.8 +/- 14.4%). The percentages of the D16+ NK cells did not change, indicating an enhanced cytotoxic capability per individual NK cell. Insulin also slightly increased the activity of NK cells in vitro. A decline at step II in the concentrations of monocytes (0.29 +/- 0.09 versus 0.12 +/- 0.03 x 10(9)/L), lymphocytes (1.57 +/- 0.46 versus 1.22 +/- 0.25 x 10(9)/L), and CD16+(24.2 +/- 17.5 versus 16.7 +/- 11.2 x 10(7)/L), CD14+ (20.9 +/- 10.8 versus 8.6 +/- 3.9 x 10(7)/L), HLA-DR+ (37.2 +/- 22.1 versus 19.2 +/- 10.7 x 10(7)/L) and CD45RO+ (91.6 +/- 33.4 versus 61.7 +/- 6.4 x 10(7)/L) cells as well as in the percentages of CD14+ cells (11.2 +/- 4.7 versus 6.4 +/- 2.3%) and CD14+/HLA-DR+ monocytes (9.7 +/- 3.9 versus 4.8 +/- 2.8%) were observed. No changes were found at step I. Hyperinsulinaemia did not change the percentages of the CD3+, CD4+, CD8+, CD19+, CD56+, CD11a+, CD45RO+ and CD45RA+ cells, the numbers of circulating immunoglobulin (Ig)G-, IgA- and IgM- secreting cells, or the proliferative responses of BMNC to phytohaemagglutinin, purified derivative of tuberculin or interleukin (IL)-2. Hyperinsulinaemia did not change the in-vitro sensibility to insulin. In conclusion, supraphysiological insulin levels increased the activity of the individual NK cells, but decreased the numbers of NK cells, lymphocytes and activated monocytes. The findings are presumably of minor clinical relevance but may indicate an insulin-induced immune activation.

The role of NK cell activity in the pathogenesis of poly I:C accelerated and spontaneous diabetes in the diabetes prone BB rat

The development of insulin dependent diabetes mellitus (IDDM) and diabetes in the diabetes prone (DP) BB rat animal model of IDDM is thought to be due to an autoimmune process. Natural killer (NK) cells have been implicated but not proven to play a pathogenetic role in BB rats due to the increased NK cell number and activity found in these animals. We have recently reported that poly I:C, an inducer of cytokines and a potent enhancer of NK cell function, accelerates the development of diabetes in DP BB rats and induces diabetes in diabetes resistant (DR) BB rats. Since we have further demonstrated that poly I:C administration to BB rats increases NK cell number and levels of inducers of NK cell activity, interferon-alpha and IL-6 which is described therein, we tested the hypothesis that NK cell activity plays an important role in poly I:C accelerated disease. The role of NK cells in poly I:C accelerated diabetes and spontaneous diabetes was examined by determining whether selective depletion of NK cells using a rat NK cell specific antibody (anti-NKR-P1 antibody) alters the development of diabetes. The treatment of BB rats with anti-NKR-P1 antibody resulted in a significantly lower mean NK cell activity of splenic mononuclear cells than that found in control animals. However, the development of diabetes and degree of insulitis was not significantly different between treatment groups. BB rats administered anti-NKR-P1 antibody with poly I:C had a lower mean splenocyte NK cell activity and lower mean NK cell number within the peripheral blood and inflamed islets than rats administered poly I:C alone. However, anti-NKR-P1 antibody administration did not alter the accelerated development of diabetes or the degree of insulitis in poly I:C treated animals. These data document that NK cells do not play a major role in the pathogenesis of poly I:C accelerated diabetes or spontaneous diabetes in the DP BB rat.

Adoptive transfer of diabetes to and from old normoglycaemic BB rats

Approximately 4% of diabetes-prone BB/Mol rats escape overt diabetes which occurs in other rats between 56 and 130 days of age. The ability of preactivated spleen cells from older non-diabetic and from acutely diabetic rats to adoptively transfer diabetes into young diabetes-prone rats was compared, and it was found that they transferred disease with similar incidence and with overlapping onset times in the recipients. Old non-diabetic rats were themselves susceptible to diabetes adoptively transferred from acutely diabetic or from old nondiabetic donors. Lymphocytic insulitis and pancreatic insulin content in unmanipulated old non-diabetic rats were both intermediate between those seen in acutely diabetic and in diabetes-resistant rats. In vivo treatment with polyinosinic-polycytidylic acid induced diabetes with faster onset in old non-diabetic rats than in young diabetes-prone rats. Adoptive transfer of fresh, whole spleen cells from old nondiabetic rats did not protect young BB rats against spontaneous diabetes, while cells from diabetes-resistant rats did. Spleens from old non-diabetic rats contained significantly lower percentages of T cells than spleens from acutely diabetic rats but not lower than spleens from age-matched diabetic rats, suggesting that this reduction was age-related. Finally, spleens from both old non-diabetic and from acutely diabetic rats were negative for the regulatory RT6+ T-cell subset. It is concluded that quiescent beta-cell autoimmunity seen in a fraction of BB/Mol rats can be reactivated upon non-antigen-specific immune stimulation.

The BBZ/Wor rat: clinical characteristics of the diabetic syndrome

The BBZ/Wor rat is a model of obesity and autoimmune diabetes mellitus developed by crossing the BB/Wor and Zucker rats. We studied circulating glucose and insulin levels, islet morphology and lymphocyte subsets in lean and obese BBZ/Wor rats before and after the onset of diabetes, and studied the clinical course of diabetes in animals after interruption of exogenous insulin therapy. Lean BBZ/Wor rats developed insulin-dependent diabetes and died in ketoacidosis within 1 week after cessation of insulin injections. Diabetes also developed in obese rats, but these animals were not insulin-dependent and survived for months without insulin therapy. The islets of the lean diabetic rats revealed complete destruction of pancreatic beta cells and plasma insulin levels were virtually undetectable. In contrast, the islets of the obese rats revealed insulitis and substantial beta-cell loss, however autoimmune beta-cell destruction was incomplete, and residual beta cells were presumably responsible for the presence of measurable levels of plasma insulin and the long-term survival of obese diabetics without insulin therapy. Obese rats were hyperinsulinaemic, developed diabetes significantly earlier, and with a greater incidence than lean rats, suggesting a possible relationship between enhanced beta-cell metabolic activity and immune destruction. Obese males became diabetic more frequently and at an earlier age than obese females and lean rats of both sexes, suggesting a role for gender in the pathogenesis of diabetes. We conclude that the BBZ/Wor rat is a unique animal model for investigating the interaction of obesity, beta-cell metabolism, autoimmune insulitis and genetic predisposition to diabetes.

Natural killer cell depletion and diabetes mellitus in the BB/Wor rat (revisited)

The BB/Wor diabetes-prone rat is an animal model of human insulin-dependent diabetes mellitus. In this model of spontaneous autoimmunity, natural killer cells are candidate cytotoxic effector cells, believed to be the mediators of beta-cell cytolysis in vivo. We therefore studied the effects of an anti-natural killer cell monoclonal antibody on the spontaneous development of diabetes in the BB/Wor rat. The 3.2.3 monoclonal antibody recognizes a molecular present on rat natural killer cells and selectively depletes these cells in vivo. Chronic treatment of diabetic-prone rats with 3.2.3 monoclonal antibody cleared circulating phenotypic natural killer cells, depleted in vitro spleen natural killer cell function, and profoundly reduced intra-islet accumulation of 3.2.3+ cells, but did not prevent or delay the onset of diabetes. These results indicate that natural killer cells are not necessary for the development of spontaneous diabetes in BB/Wor rats.