DBA-lpr/lpr mice mount a robust T-cell response to collagen. DBA-lpr/lpr lymphocytes show increased proliferation (a) and increased IFN-γ production (b) in response to in vitro stimulation by collagen II. Draining lymph nodes were obtained from DBA-lpr/lpr (white bars; n = 3) and control DBA-lpr/+ (filled bars; n = 3) mice 7 days after immunization with collagen II and complete Freund's adjuvant. For measurement of cell proliferation, the cells were cultured for 60 hours with collagen II at the indicated concentrations, and then pulsed with [3H] thymidine. Concentrations of IFN-γ in the supernatant were determined by ELISA. The columns represent mean values and the error bars indicate standard deviations. Differences were statistically significant in all comparisons (*P < 0.05; **P < 0.001). The enhanced T-cell response is not due to changed subpopulations. (c) Phenotypic analysis of surface expression of CD44 on nonstimulated (cC) and stimulated (cB, cD) T lymphocytes purified from lymph nodes of homozygotes (DBA/1J-lpr/lpr) (bright line) and their heterozygote (DBA/1J-lpr/+) littermates (dark line). Lymph node cells were stimulated with concanavalin A (cB) and bovine collagen II (cD). The isotype control is shown as shadowed area. The samples were analyzed on a FACScan (Becton Dickinson) and gated on lymphocytes (cA).