Evaluation of in vivo Cytokine Expression in EAU-susceptible and Resistant Rats: a Role for IL-10 in Resistance?

Abstract

Messenger RNAs for six cytokines (IL-12p40, IFN-γ, IL-10, IL-4, TNF-α and TGF-β1) expressed in vivo during development of experimental autoimmune uveitis (EAU) were quantitated by PCR in (uncultured) peripheral lymphoid cells and in the eyes of EAU-susceptible Lewis and EAU resistant F344 rats. Disease was induced by immunization with the R16 peptide of IRBP (in RT1Blhaplotype rats) or with whole IRBP (in all haplotypes). In the periphery, both Lewis and F344 expressed similar cytokine patterns. In ocular tissues, however, only Lewis expressed elevated type 1 and inflammatory cytokines (IL-12p40, IFN-γ and TNF-α), coincident with onset and peak of disease. Interestingly, naive F344 rats expressed higher basal levels of IL-10 mRNA in the eyes. To examine the possible involvement of this phenomenon in resistance, basal levels of IL-10 vs susceptibility to IRBP were compared in Lewis, BN, DA, F344 and ACI strains. Lewis, BN and DA were susceptible and had low levels of IL-10 mRNA in eyes. F344 and ACI were resistant and expressed high basal levels of IL-10 mRNA. In an in vitro study, recombinant rat IL-10 (but not human or mouse IL-10) suppressed lymphocyte proliferation and IFN-γ production by primed lymph node cells of R16 immunized rats, but did not suppress uveitogenic long-term T-cell lines polarized to the Th1 phenotype, suggesting that mature effector lymphocytes in the rat may lose their ability to be suppressed by IL-10. We propose that higher expression of the IL-10 gene in ocular tissues in some rat strains may represent a mechanism that contributes to a higher threshold of resistance to EAU, but this threshold may be overcome by a more mature Th1 effector with a reduced sensitivity to IL-10.