B cells are selectively associated with thymic cortical but not medullary pathology in NZB mice

Reduced thymic Aire expression and abnormal NF-kappa B2 signaling in a model of systemic autoimmunity

The thymic stromal niche normally directs the production and export of a self-tolerant T cell repertoire. Many models of spontaneous autoimmunity, however, develop thymic architectural abnormalities before disease onset. Although this is suspected to affect central tolerance induction, creating an autoimmune predisposition, in-depth analysis of the microenvironment within these thymi is lacking, such that the mechanisms and likely direct effects on the T cell repertoire are unknown or speculative. Here we show that NZB mice, the first described model for systemic autoimmunity, demonstrate a complex thymic phenotype, including a lack of the autoimmune regulator (Aire), early defects in thymic epithelial cell (TEC) expansion, and evidence for altered NF-kappaB2 signaling. Analysis of medullary TEC revealed a numerical loss of the Aire-expressing MHC class II(high) (mTEC-high) subset as well reduced Aire protein and mRNA per cell. RelB expression was also reduced, while chemokines CCL19 and CCL21 were increased. Unexpectedly, the proportion of cortex and medulla in the NZB mice was normal from 36 wk, despite worsening architectural abnormalities. These data show that the NZB defect is more complex than previously appreciated, segregating into early numerical TEC deficiencies that correct with age, late degeneration of the niche architecture that does not affect TEC number, and a persistent reduction in Aire and RelB expression per cell acquired upon mTEC-high differentiation.

The diabetes-prone NZO/HlLt strain. I. Immunophenotypic comparison to the related NZB/BlNJ and NZW/LacJ strains

New Zealand Obese (NZO)/HlLt male mice exhibit a polygenic obesity and approximately 50% develop type 2 diabetes. This strain is known to produce a variety of autoantibodies, including autoantibodies to the insulin receptor. Because of their relatedness to the autoimmune-predisposed New Zealand Black (NZB) and New Zealand White (NZW) inbred strains, we compared NZO to its two related strains for shared hematologic and immunologic characteristics. Comparison of the three strains by serotyping and genotyping methods indicated that NZO shared with NZW the rare (recombinant) H2(z) haplotype at the major histocompatibility complex. Similar to the NZB and NZW strains, spleens from NZO mice contained increased numbers of CD19(+)CD43(+) IgM(+) B-1 B cells, a phenotype associated with natural autoantibody production. NZO mice developed a progressive microcytic anemia that was distinguished from NZB hemolytic anemia by absence of demonstrable antierythrocyte antibodies in the former. Outcross of NZO females with NZB males accelerated development of obesity and diabetes in F1 males. NZO males made B-lymphocyte-deficient by a disrupted immunoglobulin heavy chain gene did not become diabetic. These results suggest that NZO mice should be useful to investigators interested in studying the genetic contributions to autoimmunity made by the related NZW and NZB strains. Further, these results, combined with the pancreatic histopathology contained in the companion manuscript, suggest that B lymphocytes may be important contributors to diabetes pathogenesis in the NZO mouse.

The diabetes-prone NZO/Hl strain. II. Pancreatic immunopathology

We report the first combined light and electron microscopic analysis of the pancreas during the development of type 2 diabetes in the New Zealand Obese (NZO) mouse. As in most other polygenic rodent models of type 2 diabetes, hyperglycemia associated with beta cell destruction is male sex-limited. Increasing degrees of hyperinsulinemia and transition to diabetes were clearly reflected by the islet volume fraction, by the beta cell granulation state, and by ultrastructural changes, primarily of the endoplasmic reticulum. One of the unusual histopathologic features of NZO mice of both sexes was the presence of B-lymphocyte enriched leukocytic aggregates in the pancreas. Immunocytochemical analysis of the pancreas of 52-week-old diabetic males indicated enrichment for CD19(+) B lymphocytes. Staining of adjacent sections for CD3 and CD5 indicated CD5 coexpression on some of the CD19(+) cells, suggesting the presence of the B1-B subset associated with generation of natural autoantibodies in other autoimmune-prone New Zealand mouse strains. In addition, plasma cells in peri-insular leukocytic infiltrates were identified by electron microscopy. Hence, although autoimmunity has previously proven to be a secondary manifestation of beta cell destruction in most rodent models of type 2 diabetes, the present observations suggest that B lymphocyte function, in association with male gender, may contribute to the development of insulin resistance and chronic hyperglycemia in the NZO model.