Characterisation of cartilage intermediate layer protein (CILP)-induced arthropathy in mice.

OBJECTIVES To characterise cartilage intermediate layer protein (CILP)-induced arthropathy in mice. METHODS The first and second halves of the nucleotide triphosphate pyrophosphohydrolase (NTPPHase) non-homologous region of human CILP were prepared as recombinant proteins (C1 and C2, respectively), including three overlapping fragments of C2 (C2F1, C2F2, and C2F3). C57BL/6 mice were immunised with these proteins to induce arthritis. In addition, a separate group of mice were immunised repeatedly with the mixture of C1 and C2 to see the effect of chronic immunisation. Arthritis developed in the mice, and cellular and humoral immune responses against CILP were analysed. RESULTS Immunisation with C2 and with the mixture C2F1/C2F2/C2F3 caused the severest arthritis to develop in mice. Immunisation with one of C1, C2F1, C2F2, or C2F3 caused milder arthritis, even though each of the fragments carried T cell epitopes. Immunisation either with C1 or C2 alone evoked cellular and humoral immune responses to both the C1 and C2 proteins. Further, the repeated immunisation with the C1/C2 mixture caused tendon calcification and bone irregularity, together with decreased NTPPH activity. CONCLUSIONS The results show that multiple T cell epitopes are needed for the development of CILP-induced arthritis, and present the characteristic new model of mild arthropathy accompanied by extra-articular calcifications. An immune response to putative murine CILP/NTPPH may be involved in the ectopic calcifications in the arthritic mice.