Characterization of G6PI-induced arthritis. Shown are characteristics of glucose-6-phosphate isomerase (G6PI)-induced arthritis in different genetic backgrounds and major histocompatibility complex (MHC) congenics. (a) DBA/1 mice were immunized intradermally at the base of the tail with the indicated amounts of G6PI emulsified in complete Freund's adjuvant (CFA) to establish a dynamic immunization protocol allowing for an increase or decrease in disease severity. The course of disease was followed for 40 days after immunization. The graph shows the mean scores for all mice. Disease developed in 8/8 (400 μg/mouse), 9/9 (200 μg/mouse) and 8/9 (100 μg/mouse) mice. (b) After establishing the immunization protocol, mice with different MHC haplotypes and genetic backgrounds were immunized with 200 μg G6PI in CFA at the base of the tail. Active arthritis, characterized by redness and oedema, was scored over 90 days after immunization. Blood was drawn at day 40 for antibody analysis and the mice were boosted with human G6PI (50 μg/mouse in incomplete Freund's adjuvant) at day 48. The numbers of mice of each strain evaluated were as follows: (B10.Q × DBA/1)F1, n = 10; B10-Tg(DR4), n = 8; B10.P, n = 12; B10.Q, n = 26; B10.RIII, n = 6; C3H.NB, n = 9; and DBA/1, n = 10. (c) Because the MHC haplotype H-2p on the black background rendered mice resistant to G6PI-induced arthritis, the role of the beta chain of Ap was addressed on the highly susceptible C3H background. C3H.NB (H-2p; n = 21) and C3H.Q (H-2q; n = 19) mice were immunized intradermally with 200 μg G6PI in CFA and scored for 73 days. At no time point was a significant difference noticed between the two MHC congenic strains. Only a tendency toward more chronic progression could be seen in the C3H.Q mice during the late phase. In all experiments, error bars indicate the standard error of the mean.