Autologous dendritic cells stimulate human HSP60 responsive T cells, in the absence of additional exogenous antigen

Background

Animal models and clinical studies of inflammatory arthritis have shown a potentially protective role for autoreactive T lymphocytes recognising the 60 kilodalton heat shock protein (hsp60). The mechanisms of this protection have not been fully characterised. We have previously demonstrated that PBMC from healthy individuals show proliferative responses to human hsp60, and clones have been isolated that recognise the self protein. The objective of the present study was to confirm the autoreactive nature of these cells and determine whether the endogenous antigen could be effectively presented by professional antigen presenting cells.

Methods and results

Highly purified recombinant human hsp60 was prepared along with a non-recombinant preparation of mitochondrial hsp60, derived from human lymphoblastoid cells. To assess the ability of professional antigen presenting cells to present the endogenous self hsp60, autologous dendritic cells were isolated from peripheral blood by negative selection, cultured in GM-CSF and IL-4, and activated with LPS prior to use. Human hsp60 responsive T cell clones from a healthy individual were shown to proliferate in response to both the recombinant preparation and the mitochondrial preparation, thereby excluding the possibility of the clones recognising bacterial contaminants. Furthermore these clones proliferated in the presence of autologous dendritic cells, activated with LPS, in the absence of exogenous antigen. The proliferative responses to the activated dendritic cells were titratable and the data suggested a requirement for additional, presumably apoptotic, cells to also be present in the culture system.

Conclusions

These experiments demonstrate, at a clonal level, an autoreactive repertoire in healthy individuals responding to human hsp60. The ability of these cells to recognise autologous activated dendritic cells may provide insight into the role of such cells in vivo. Since activated dendritic cells and increased numbers of apoptotic cells will both be present at inflammatory foci, local expansion of potentially immunomodulatory, self hsp60 responsive T cells could occur at these sites.