Nonvascularized xenograft rejection is T cell mediated, but is dependent on initial macrophage (Mφ) infiltration. We developed an i.p. transplant model to define the roles of Mφ and T cells in xenograft rejection. Nonobese diabetic or BALB/c mice were injected i.p. with xenogeneic, allogeneic, or syngeneic cells, and the responding cells in subsequent lavages were assessed by flow cytometry and adoptive transfer. Neutrophils and monocytes/elicited Mφ were rapidly recruited in response to xenogeneic pig (PK15 or spleen) cells and, to a significantly lesser extent, allogeneic cells. These innate responses preceded T cell infiltration and occurred in their absence in SCID mice. Syngeneic cells induced negligible neutrophil or Mφ responses. Neutrophils and Mφ induced by xenogeneic cells in SCID mice stimulated T cell recruitment after transfer to immunocompetent mice. T cells in turn were required for Mφ activation and xenogeneic cell rejection. Thus, Mφ harvested from immunocompetent but not SCID mice injected with xenogeneic cells expressed activation markers and rejected xenogeneic cells when transferred into SCID mice. These findings demonstrate the interdependent roles of Mφ and T cells in xenograft rejection. The requirement for Mφ reflects their ability to mount a rapid, local innate response that stimulates T cell recruitment and, having received T cell help, to act as direct effectors of rejection.

Rotavirus infection in children at risk of developing type 1 diabetes has been temporally associated with development of pancreatic islet autoantibodies. In this study, nonobese diabetic mice were shown to be susceptible to rhesus rotavirus infection and pancreatic islets from nonobese diabetic mice, nonobese diabetesresistant mice, fetal pigs, and macaque monkeys supported various degrees of rotavirus growth. Human rotaviruses replicated in monkey islets only. This islet susceptibility shows that rotavirus infection of the pancreas in vivo might be possible.Rotaviruses are the major cause of human infantile gastroenteritis worldwide, with multiple serotypes causing regular winter outbreaks until herd immunity is almost complete by 5 years of age (4). These nonenveloped, triple-layered, doublestranded RNA viruses are members of the family Reoviridae (13). Their outer capsid is composed of the glycoprotein VP7, through which spikes of the protein VP4 protrude (45). Both VP4 and VP7 independently elicit neutralizing, protective antibodies and are serotype determinants (40). VP4 is an important determinant of virulence, host cell tropism (28), receptor binding, and cell penetration (31,35). Proteolytic cleavage by pancreatic trypsin of VP4 into two subunits, VP8‫ء‬ and VP5‫,ء‬ is required for virus infectivity and promotes rapid virus internalization into the cell. VP6 forms the capsid underlying the outer capsid and determines group and subgroup specificity (13).Rotaviruses normally infect the mature enterocytes of the small intestine but may spread extraintestinally. Indications of rotavirus infection of the liver in humans include elevated liver aminotransferase activity during rotavirus infection (17), rotavirus particles in a liver abscess (18), and rotavirus replication in HepG2 cells (32,52). In children with severe combined immunodeficiency (SCID) and chronic rotavirus infection, replicating rotavirus is present in the liver and kidneys and rotavirus antigen is detectable in the serum (16, 51).Severe rotavirus gastroenteritis has been associated with pancreatitis in two children (12, 39) and with nonketotic hyperglycemic syndrome in one child (48). Extraintestinal rotavirus detection in these children was not attempted. Pancreatic islet cell autoantibodies were detected in acute-phase but not convalescent-phase serum from one child (39). These antibodies are markers of islet autoimmunity and predict the T-cellmediated destruction of islet ␤ cells, leading to type 1 diabetes (T1D). In addition to islet cell autoantibodies, the subclinical autoimmune prodrome of T1D is characterized by circulating autoantibodies to insulin, glutamic acid decarboxylase (GAD), and tyrosine phosphatase-like islet antigen 2 (IA-2) (20). We detected autoantibodies to GAD and to IA-2 in acute-and/or convalescent-phase sera of 3 (30%) of 10 children without a family history of diabetes who were hospitalized with rotavirus gastroenteritis (24). This rate was at least four times that observed in normal schoolchildren (2).The strong en...

Chemically-induced diabetic mice and spontaneously diabetic NOD mice have been valuable as recipients for experimental islet transplantation. However, their maintenance often requires parenteral insulin. Diabetogenic chemicals can be cytotoxic to the host’s immune system and to other organs some of which are often used as the transplant site. Procurement of diabetic cohorts in the NOD mouse is problematic due to variability in the age of disease onset. We show that RIP-Kb mice, which spontaneously develop non-immune diabetes due to over-expression of the H-2Kb heavy chain in beta cells, offer many advantages as islet transplant recipients. Diabetes is predictable with a relatively narrow range of onset (4 wk) and blood glucose levels (23.0± 4.0 mmol/l for 39 males at 6 weeks of age). The diabetes is mild enough so that most diabetic mice can be maintained to 40 weeks of age without parenteral insulin. This consistency of diabetes avails that outcomes of intervention can be interpreted with confidence.

Previous studies on the contribution of T cell-dependent antibody (Ab) to non-vascular xenograft rejection have yielded conflicting results, being confounded by the presence of recipient T cells and the use of different tissues and immunizing regimens to generate Ab. In the present study, the effect of adoptive transfer of Ab on fetal pig pancreas (FPP) and pig PK15 cell xenografts was examined in T cell-deficient severe combined immune deficiency (SCID) mice. T cell-dependent Abs raised by hyperimmunization with different cell types and by FPP transplantation were compared. Ab raised by hyperimmunization with pig thymocytes exhibited strong binding to pig thymocytes and PK15 cells but did not transfer FPP rejection. IgG1 and IgM, but not IgG3, Abs bound strongly to FPP exocrine and connective tissue, whereas binding to endocrine cells in vitro and in vivo was weak or absent. This pattern of Ab binding was similar to that observed after transplanting FPP into BALB/c mice. Furthermore, serum recovered from BALB/c mice 20 days after FPP transplantation bound strongly to non-endocrine but not endocrine cells and did not transfer FPP rejection. In contrast, serum from mice hyperimmunized with PK15 cells bound strongly to PK15 cells and transferred rejection of intraperitoneal PK15 cells. Furthermore, this serum contained IgG1 and IgM Abs that bound strongly, and IgG3 Abs that bound weakly, to endocrine cells in FPP, and also transferred rejection of FPP in SCID mice. These results indicate that endocrine cells express low concentrations of xenoreactive Ab epitopes and that high Ab concentrations and/or high avidity Abs are required for sufficient endocrine cell binding to cause damage and rejection in the immunodeficient mouse model. Such Abs are not elicited by transplanting FPP into immunocompetent mice. Nevertheless, a contribution of Ab to rejection in immunocompetent mice cannot be excluded.