T and B lymphocytes of mice immunized with carbamylated peptide (Hcit) predispose to Cit-induced arthritis. CD3+ and CD19+ cells were isolated by negative selection from the spleens of Hcit-immunized BALB/c mice and injected i.v into naive BALB/c recipients (5 × 106 cells/mouse, n = 10). Control BALB/c mice received the same number of CD3+ or CD19+ cells isolated from naive BALB/c mice (n = 10). On day 12 following lymphocyte transfer, all mice received intra-articular injections of Cit-peptide (1 μg/knee). A, Histological evaluation of injected knee joints 7 d later showed development of severe arthritis in 100% of the recipients of CD3+ cells from Hcit-immunized mice (arthritis index, 2.19 ± 0.54) (1, 3), whereas only two recipients of naive CD3+ cells showed evidence of arthritis (arthritis index, 0.4 ± 0.41; p = 0.003) (2, 3). Knees were embedded in paraffin, sectioned, and stained with H&E. Original magnification ×500. B, Recipients of Hcit-immunized CD3+ cells also showed a significant increase in the T cell proliferation rate (p < 0.0001) (1) and produced more IFN-γ compared with controls (2). C, Recipients of Hcit-immunized CD3+ or CD19+ cells showed significantly higher levels of Hcit-specific Abs, as assessed by ELISPOT. Values represent mean ± SEM. Horizontal lines indicate the median.