The type of collagen cross-link determines the reversibility of experimental skin fibrosis.

Fibrotic processes in humans are characterised by an excessive accumulation of collagen containing increased levels of hydroxyallysine-derived cross-links. The occurrence of these cross-links appears to be an important criterion in assessing the irreversibility of fibrosis. We hypothesise that increased hydroxyallysine cross-linking results in a collagenous matrix that is less susceptible to proteolytic degradation and therefore the collagen deposition is no longer reversible. In this report, we show that collagen matrices with increased hydroxyallysine cross-link levels were less susceptible to matrix metalloproteinase 1 degradation than are collagen matrices containing low hydroxyallysine levels. These data indicate that the type of collagen cross-link influences collagen catabolism. In vivo evidence for the importance of the cross-linking type in determining the reversibility of the fibrotic process was found using the bleomycin-induced skin fibrosis mouse model. The analysis of the accumulated collagen in the fibrotic skin of bleomycin-treated mice did not reveal an increase in hydroxyallysine cross-link levels. In concurrence with our hypothesis, the collagen accumulation resolved in time when the mice were no longer receiving bleomycin treatment, showing the reversibility of the fibrosis. In conclusion, our data indicate that the type of collagen cross-linking is an important factor in determining whether the outcome of the fibrotic process is reversible or not.

FcR interactions do not play a major role in inhibition of experimental autoimmune encephalomyelitis by anti-CD154 monoclonal antibodies.

It has been demonstrated that anti-CD154 mAb treatment effectively inhibits the development of experimental autoimmune encephalomyelitis (EAE). However, although it appears to prevent the induction of Th1 cells and reactivation of encephalitogenic T cells within the CNS, little information is available regarding the involvement of alternative mechanisms, nor has the contribution of Fc effector mechanisms in this context been addressed. By contrast, efficacy of anti-CD154 mAbs in models of allotransplantation has been reported to involve long-term unresponsiveness, potentially via activation of T regulatory cells, and recently was reported to depend on Fc-dependent functions, such as activated T cell depletion through FcgammaR or complement. In this study we demonstrate that anti-CD154 mAb treatment inhibits EAE development in SJL mice without apparent long-term unresponsiveness or active suppression of disease. To address whether the mechanism of inhibition of EAE by anti-CD154 mAb depends on its Fc effector interactions, we compared an anti-CD154 mAb with its aglycosyl counterpart with severely impaired FcgammaR binding and reduced complement binding activity with regard to their ability to inhibit clinical signs of EAE and report that both forms of the Ab are similarly protective. This observation was largely confirmed by the extent of leukocyte infiltration of the CNS; however, mice treated with the aglycosyl form may display slightly more proteolipid protein 139-151-specific immune reactivity. It is concluded that FcR interactions do not play a major role in the protective effect of anti-CD154 mAb in the context of EAE, though they may contribute to the full abrogation of peripheral peptide-specific lymphocyte responses.