BALB/c mice genetically susceptible to proteoglycan-induced arthritis and spondylitis show colony-dependent differences in disease penetrance

Table 2 Immunological differences between arthritic and non-arthritic animals as well as mice with or without spondylitis

Measured parameters	Arthritic animals (n = 154)	Non-arthritic animals (n = 24)	Mice with spondylitis (n = 80)	Mice without spondylitis (n = 47)
In vitro T-cell proliferation, SI	2.96 ± 0.07	3.25 ± 0.13	3.00 ± 0.09	3.00 ± 0.14
In vitro IL-2 production (CTLL-2), SI	2.67 ± 0.07	2.73 ± 0.15	2.68 ± 0.10	2.66 ± 0.11
In vitro IL-4 production, ng/10⁶ cells	2.65 ± 0.14	2.91 ± 0.34	2.79 ± 0.22	2.39 ± 0.18
In vitro IL-6 production, ng/10⁶ cells	1.83 ± 0.01	2.17 ± 0.33	1.88 ± 0.14	1.86 ± 0.19
In vitro IFN-γ production, ng/10⁶ cells	8.06 ± 0.28	8.50 ± 1.07	7.61 ± 0.37	9.56 ± 0.65^a
In vitro TNF-α production, ng/10⁶ cells	0.74 ± 0.01	0.77 ± 0.02	0.74 ± 0.01	0.75 ± 0.02
Serum IL-4, pg/mL	15.29 ± 2.41	22.80 ± 5.92	15.52 ± 3.32	18.49 ± 4.46
Serum IL-6, pg/mL	166.45 ± 20.21	106.18 ± 26.97	97.59 ± 14.94	65.05 ± 20.61
Serum IL-1β, pg/mL	96.36 ± 11.55	41.70 ± 11.29	163.78 ± 27.72	143.10 ± 31.16
Serum IFN-γ, pg/mL	26.14 ± 2.62	34.59 ± 6.27	25.05 ± 3.65	33.49 ± 4.55
IgG1 antibodies to human PG, mg/mL	12.75 ± 0.57^b	8.30 ± 0.94	23.33 ± 0.78^b	8.85 ± 0.86
IgG2a antibodies to human PG, mg/mL	1.36 ± 0.14^a	0.72 ± 0.29	1.44 ± 0.21^a	0.82 ± 0.17
IgG1 antibodies to PG, μg/mL	172.55 ± 13.47^b	76.41 ± 10.56	174.99 ± 18.95^a	116.68 ± 17.7
IgG2a antibodies to PG, μg/mL	68.01 ± 5.68^b	24.79 ± 6.76	72.10 ± 8.18^b	34.57 ± 6.16

All animals were immunized simultaneously with human cartilage proteoglycan in dimethyldioctadecyl-ammonium bromide. A total of three injections were given at 3-week intervals, and mice were sacrificed 3 weeks after the third injection (on days 63 and 64) when all in vitro assays were performed. Values represent mean ± standard error of the mean. Histological analysis was performed, and each inflamed intervertebral disc (IVD) was scored from '0' to '8' as described in Materials and methods. Positive (spondyloarthopathic) animals were combined if at least one IVD was affected with inflammation. Superscript letters indicate the level of significance (^aP < 0.05 and ^bP < 0.01) between arthritic and non-arthritic animals or between mice with or without spondylitis. IFN-γ, interferon-gamma; IL, interleukin; PG, proteoglycan; SI, stimulation index; TNF-α, tumor necrosis factor-alpha.

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