Pathogenesis of collagen-induced arthritis: modulation of disease by arthritogenic T-cell epitope location.

Collagen-induced arthritis (CIA) is an animal model of human rheumatoid arthritis that can be induced in susceptible mice by immunization with type II collagen (CII) or with collagen fragments, including cyanogen bromide (CB) peptides. One susceptible mouse strain, B10.RIII (I-Ar), has previously been found to respond to two major T-cell determinants, namely CII 610-618 (GPAGTAGAR) within CB10 and CII 445-453 (GPAGPAGER) within CB8. Although CB10 contains the immunodominant determinant, it is not arthritogenic. Using recombinant techniques, the determinant within CB10 was mutated to rCB10(T614P,A617E), generating a recombinant CB10 that in effect contained the arthritogenic epitope. When used for immunization, rCB10(T614P,A617E) was arthritogenic. This suggested that the arthritogenic property was intrinsic to the epitope and unrelated to its position within the CII molecule. To test this hypothesis, additional mutants were generated. The wild-type T-cell epitope of CB10 was deleted from its natural position, and the 'arthritogenic' GPAGPAGER T-cell epitope was inserted into the C-terminal portion of the CB10 peptide. The resulting peptide induced arthritis in B10.RIII mice. Adding a second copy of the T-cell determinant to other sites within CB10, however, had varying results. A second T-cell epitope located at the C-terminus of rCB10 significantly increased the incidence and severity of arthritis, while determinants placed in other positions had little effect. These data indicate that the T-cell epitope has intrinsic arthritogenic properties, but there are positional and structural constraints that affect its arthritogenicity. Enhanced arthritis was associated with an increased T-cell proliferation to the peptides, an increase in the level of inflammatory cytokines, and higher levels of anti-CII immunoglobulin. These data suggest that the position and copy number of T-cell determinants also affect the overall immune T-cell responses.