In the present study, we explored the possibility of using recently identified MMP T-cell epitopes for immunotherapy in AA. First, we monitored T-cell responses to the MMP epitopes during the course of AA. In general, low proliferative responses to these epitopes were detected, which were accompanied by specific DTH reactions. We have previously shown that the proliferative response to mycobacterial 65 kDa heat-shock protein (hsp65) 178–186, which is the dominant epitope recognized by arthritogenic T cells in AA [9
], is also very low when tested in a polyclonal lymph node cell population [9
] (Fig. ).
To analyze whether the low MMP-specific proliferative responses are due to, for example, low precursor frequency or tolerance, it would be necessary to isolate and further characterize the MMP-specific T cells. We are currently developing a specific T-cell capture assay based on liposomal-bound MHC–peptide complexes to isolate such cells [15
]. Interestingly, although the MMP epitopes greatly differed in MHC class II RT1.BL
binding affinity, no differences in DTH reaction and/or proliferation were observed, indicating that these epitopes become a target for T-cell recognition irrespective of their MHC binding affinity. It was previously suggested that immunotherapy is most successful with high-affinity MHC binders [16
]. However, the present study shows that the strongest immunomodulatory peptide, MMP-10329–343
, was a weak MHC class II RT1.BL
The upregulation of MMP-3 and its pathogenic role in arthritis has been shown in numerous reports, while only a few reports describe the presence of MMP-10 and MMP-16 in the synovium of RA patients [17
]. Although MMP-10 and MMP-16 have been suggested to be involved in connective tissue/bone remodeling around prostheses [19
], their role in arthritis is less clear. Surprisingly, peptides derived from MMP-10 and MMP-16, but not from MMP-3, can alter the course of AA after nasal administration. The observed opposite effect of nasal therapy using MMP-10 peptide furthermore illustrates that we seem to target the proper cell population to interfere in arthritis, but that the desired disease inhibitory effect strongly depends on the timing of T-cell modulation.
Other studies have also shown that mucosal therapy might in some cases induce or even exacerbate T helper 1 cell autoimmunity [21
]. Moreover, the critical aspect of proper timing has also been described for cytokine therapies as shown by both disease inhibition and exacerbation after in vivo
administration of IFN-γ, IL-2 or IL-12 in experimental arthritis models [24
In the present study, we stated that the improvement of arthritis symptoms after MMP-10 peptide pretreatment coincided with a decreased proliferative response to the critical T-cell epitope for the induction of AA, mycobacterial hsp65178–186. Although the proliferative response to this epitope is difficult to measure in a polyclonal lymph node cell population, our results suggest that MMP-10 peptide pretreatment inhibits the response to the arthritogenic epitope via bystander suppression. Immunotherapy using agents that induce T-cell-mediated bystander suppression makes it unnecessary to identify the self-antigens involved in the initiation of the arthritis process, but makes it possible to exploit spreading epitopes or other self-antigens that become available during the arthritis process for disease intervention.