Systemic autoimmune diseases have a complicated and largely unknown etiology and pathogenesis, but they are at least partly obeying the rules of an ordinary immune response. Cytokines are therefore important in the pathogenesis as demonstrated by the recent success in treating rheumatoid arthritis with anti-cytokine agents. The suppressive fimctions in the immune system have lately received much interest. One of the cytokines in focus in this respect is IL-10. We recently observed that in heavy-metal induced systemic autoimmunity, genetically resistant mice show a strong increase in IL-10 mRNA expression, which was not seen in susceptible mice. We have therefore examined the possible regulating effect of IL-10 on induction and manifestation of systemic autoimmunity in this model. We took two approaches: a targeted mutation for the IL-10 gene in a strain resistant to heavy-metal induced autoimmunity, and treatment with recombinant IL-10 in the genetically susceptible A. SW strain during the induction of autoimmunity by metals.
The wild-type C57BL/6J (B6-WT) strain did not react with lymphoproliferation, polyclonal B-cell activation, increases in antinuclear autoantibodies (ANA) or tissue immune-complex (IC) deposits in response to inorganic mercury (Hg) or silver (Ag). However, in agreement with previous obsetvations there was a modest increase in serum IgG1, IgE and IgG2a. Treatment with Ag caused only a weak increase in IgE and IgG1. The B6.129P2-µ10tm1Cgn /J strain (IL-10 deficient B6 mice) did not develop antinucleolar antibodies (ANoA) during Hg treatment, but compared with Hg-treated B6-WT mice there was a significant increase in homogeneous ANA and a higher serum IgE concentration. The IL-10 deficient B6 controls showed a spontaneous increase in splenic weight as well as serum IgM and IgG1 compared with the B6-WT control mice. These signs of immune activation were also present in the IL-10 deficient B6 mice treated with Hg, while treatment with Ag reduced these features making the response similar to that in the B6-WT controls.
The susceptible A.SW mice treated with rIL-10 and Hg showed during ongoing intense rIL-10 treatment reduced induction of ANoA, reduction in antichromatin antibodies (ACA), and a reduced increase in serum IgE compared with mice which received Hg but not rIL-10. In conclusion, the reduced ANoA induction during riL-10 treatment indicates suppressive effect of IL-10 on autoimmune development. Lack of IL-10 may promote development of ANA, ACA, and serum IgE, but is not likely to be crucial for resistance to heavy-metal induced autoimmunity.