Reduced percentages of CD5+ B lymphocytes in severe arthritis. Type II collagen/complete Freund's adjuvant (cII/CFA)-immunized, cII T-cell receptor transgenic mice (n = 19) were scored for arthritis severity on a 3-point scale for each paw and then euthanized on day 28 after immunization. Single-cell suspensions of splenic leukocytes were stained with antibodies as described in Materials and methods and analyzed by four-color flow cytometry. Percentages of CD4+ and CD8+ T cells (among CD3+/B220- lymphocytes) and CD5+ and CD5- B cells (among CD19+ lymphocytes) within the small nongranular lymphocyte gate were plotted for individual mice versus the final disease score. Only the percentage of CD5+ B cells showed a significant decline as disease severity increased (R-squared = 0.4222, F = 11.69, P = 0.0035). Data are from a representative experiment of two experiments (n = 37 mice total).