NOD/Lt mice harboring a hybrid rat insulin-promoter/SV40 large T-antigen gene spontaneously develop β-cell adenomas. NIT-1 is a pancreatic β-cell line established from one of these transgenic mice. Immunocytochemical staining of passage 18 cells showed most contained insulin, with <5% containing glucagon, and none containing pancreatic polypeptide or somatostatin. Glucagon content radioimmunoassayed in cell extracts was only 0.27% of the insulin content. Two-hour insulin secretion at 16.5 mM glucose was 638 ng/106 cells (41% of intracellular content) compared to only 1.3 ng glucagon (32% of intracellular content). Stimulated insulin secretion was consistently observed in response to 11 and 16.5 mM glucose between passages 11 and 19. At passage 19, both theophylline and tolbutamide stimulated insulin secretion at 5.5 mM glucose. Northern-blot analysis confirmed high levels of insulin mRNA but only trace glucagon mRNA and undetectable somatostatin mRNA. Interferon-γ (IFN-β)–induced MHC class I RNA expression was correlated with markedly increased antigen expression at the cell surface. Similarly, a MHC-linked “occult” class I–like antigen detected by Cr release assay only after exposure of standard NOD/Lt islet cells to IFN-γ was strongly induced by IFN-γ in NIT-1 cells. Cell surface MHC class II antigen was not constitutively expressed on NIT-1 cells and could not be detected after IFN-γ incubation, despite demonstration of IFN-β-induced Aa, Ab, and li invariant-chain RNA transcripts. Similarly IFN-γ induction of intercellular adhesion molecule 1 (Icam-1) transcripts was not accompanied by demonstrable cell surface expression of ICAM-1 antigen. NIT-1 cells exhibited ultrastructural features typical of differentiated mouse β-cells, including numerous p-granules. An unusual finding was that NIT-1 cells were shedding mature type C retrovirus from their surfaces. Because this cell line represents a source of immortalized NOD β-cell genome, it will be useful for a wide variety of studies dealing with β-cell antigens.

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