Citrullinated proteins have increased immunogenicity and arthritogenicity and their presence in arthritic joints correlates with disease severity

Table 1 Correlation of presence of citrullinated proteins and peptidyl arginine deiminase 4 with degree of inflammation

Days after immunisation	Arthritis score	Cell infiltration	Cartilage destruction	Citrulline-positive deposits	Citrulline-positive cells	Citrulline-positive cartilage	PAD4-positive cells
0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
3	0.0	0.0	0.0	0.0	0.0	0.0	0.0
6	0.0	0.0	0.0	0.0	0.0	0.0	0.0
10	0.0	0.0	0.0	0.0	0.0	0.0	0.0
15	3.3 ± 2.4	1.3 ± 0.5	0.0	0.0	0.0	0.0	0.0
21	9.8 ± 3.3	1.8 ± 0.5	0.5 ± 0.6	1.0	0.5 ± 0.6	0.8 ± 1.0	1.0 ± 0.5
28	11.0 ± 3.5	3.0	2.5 ± 0.6	1.8 ± 1.0	1.3 ± 0.5	1.5 ± 1.3	1.5 ± 0.4
38	11.8 ± 2.6	3.0	3.0	2.7 ± 0.6	1.8 ± 0.5	0.5 ± 0.6	2.2 ± 0.5

PAD4, peptidyl arginine deiminase 4. Arthritic score, cell infiltration, cartilage destruction and presence of citrullinated proteins in extracellular deposits, cells and cartilage were evaluated at different time points of collagen-induced arthritis. All data are from four rats, evaluated in a blinded manner by two independent evaluators and are means ± SD. Arthritis score ranges from 0 to 16 as explained in the Materials and methods section. Arbitrary units were used for the other features, ranging from 0, indicating no cell infiltration, cartilage destruction, presence of citrullinated proteins or PAD4, to 3, indicating extensive cell infiltration, cartilage destruction, presence of citrullinated proteins and PAD4.

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