Anti-collagen antibodies in systemic sclerosis and in primary Raynaud's phenomenon

The frequency and specificity of antibodies to native and denatured collagens were evaluated in systemic sclerosis (SSc) and in primary Raynaud's phenomenon (PRP) by direct and competitive ELISA. Antibodies reactive with denatured collagen type I (CI) were found in 43% of the SSc sera, and anti-CIV and anti-CV in 31%. In PRP, anti-CI, anti-CIV and anti-CV antibodies were detected in 8% of patient sera. Anti-CI, anti-CIV and anti-CV antibodies reacted with determinants expressed on the native as well as on the denatured molecule. Anti-CI and anti-CIV were cross-reactive; a reactivity with CII and a lower one with CV were detected. Anti-CV antibodies also reacted with CI and CII and, in a smaller proportion of cases, with CIV. Anti-collagen antibodies, affinity-purified from blotted collagen IV and V and cyanogen bromide (CBr)-digested CI, displayed the cross-reactivities shown by inhibition studies on sera. Moreover, antibodies eluted from a CBr fragment of CI reacted with the other CBr fragments as well. These data show that one-third of SSc sera contain antibodies that react with epitopes expressed on native as well as on heat-denatured CI, CII, CIV and CV, and therefore have the potential to bind collagens in vivo.