The non-obese diabetic (NOD) mouse is a spontaneous model of human insulin-dependent diabetes mellitus. Both CD4+ and CD8+ T cells infiltrate the pancreatic islets of NOD mice prior to beta-cell destruction. T-cell lines isolated from the islets of NOD mice are tools for studying the pathogenesis of insulin-dependent diabetes mellitus. During attempts to generate such lines we isolated an autoreactive CD4+ T-cell line, designated C2, from the 'insulitis' lesion of a 20-week-old female non-diabetic NOD/WEHI mouse. Islet T cells were propagated by the addition of interleukin-2 and reexposure every 2 weeks to whole NOD islets and irradiated NOD spleen cells as antigen presenting cells. C2 cells proliferated up to 100-fold upon exposure to NOD antigen presenting cells but did not respond to whole NOD islets or antigen presenting cells from allogeneic mouse strains. Proliferation of C2 cells to NOD antigen presenting cells was blocked by a monoclonal antibody against the unique class II MHC molecule of NOD, I-Ag7. In response to NOD antigen presenting cells, C2 cells secreted interferon-gamma, tumour necrosis factor-alpha and interleukin-6 but no detectable interleukin-2, interleukin-4 or interleukin-10, a pattern of cytokine secretion more characteristic of Th1 CD4 cells. C2 cells displayed significant cytotoxicity in a redirected lysis assay. To explore a possible role for autoreactive T cells in the pathogenesis of autoimmune diabetes, C2 cells were injected i.v. into female NOD mice that had received cyclophosphamide to accelerate development of diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)