RESULTS: In the present study, the clinical and cellular responses of 24 healthy horses were monitored over 72 h after simultaneous intradermal and intramuscular application of equine
IL-12/IL-18
DNA (complexed with a transfection
reagent) or comparative substances (transfection
reagent only, nonsense
DNA, nonsense
DNA depleted of CG). Although the strongest effect was observed in horses treated with expressing
DNA, horses in all groups treated with
DNA showed systemic responses. In these horses treated with
DNA, rectal temperatures were elevated
after treatment and
serum amyloid A increased. Total leukocyte and neutrophil counts increased, while lymphocyte numbers decreased. The secretion of tumour
necrosis factor alpha (TNFα) and
interferon gamma (IFNγ) from peripheral mononuclear blood cells ex vivo increased
after treatments with
DNA, while
IL-10 secretion decreased. Horses treated with
DNA had significantly higher myeloid cell numbers and
chemokine (C-X-C motif)
ligand (CXCL)-10 expression in skin samples at the
intradermal injection sites compared to horses treated with transfection
reagent only, suggesting an inflammatory response to
DNA treatment. In horses treated with expressing
DNA, however, local CXCL-10 expression was highest and immunohistochemistry revealed more intradermal IL-12-positive cells when compared to the other treatment groups. In contrast to non-grey horses, grey horses showed fewer effects of
DNA treatments on blood lymphocyte counts, TNFα secretion and myeloid cell infiltration in the dermis.
CONCLUSION: Treatment with complexed linear
DNA constructs induced an inflammatory response independent of the coding sequence and of CG motif content. Expressing
IL-12/IL-18
DNA locally induces expression of the downstream mediator CXCL-10. The grey horses included appeared to display an attenuated immune response to
DNA treatment, although grey horses bearing
melanoma responded to this treatment with moderate tumour remission in a preceding study. Whether the different immunological reactivity compared to other horses may contributes to the
melanoma susceptibility of grey horses remains to be elucidated.