Autoimmune effects of hexachlorobenzene in the rat.

We investigated whether autoimmune disregulation underlies the formerly reported induction of IgM hypergammaglobulinemia and lymphoid organ enlargement by hexachlorobenzene (HCB) in rats. To this end blood, liver, and lymphoid organs were collected from male Wistar rats after feeding a semisynthetic diet containing 0, 500, or 1000 mg HCB/kg for 3 weeks. Sera prepared from the blood were analyzed for total and (auto)antigen-specific antibody levels by ELISA, organs were weighed, and spleens were further investigated morphologically using immunohistochemically stained cryosections. Present experiments confirmed the ability of HCB to increase total IgM, but not IgG, levels and to increase relative spleen, lymph node, and liver weights. HCB treatment elevated IgM, but not IgG, levels against single-stranded DNA, native DNA, rat IgG (representing rheumatoid factor), and bromelain-treated mouse erythrocytes that expose phosphatidylcholine as a major autoantigen. Antibody levels against the foreign antigens sheep erythrocytes, tetanus toxoid, and bovine serum albumin remained unaffected. The IgM autoantibodies proved to be polyreactive. Morphometric analysis of spleen sections showed that HCB caused a proportionally equal expansion of all splenic compartments, but when individual spleen weights were taken into account a significantly larger expansion of the predominantly B cell-containing marginal zones could be noted. The latter compartment also contained an increased number of macrophages that can be recognized by the monoclonal antibody ED3. The ability of HCB to elevate serum antibody levels against autoantigens, but not foreign antigens, indicates that HCB probably does not act by polyclonal B cell activation. The IgM isotype, the repertoire, and the polyreactivity of the serum autoantibodies suggest that HCB activates a recently described B cell subset shown to be committed to the production of these autoantibodies and associated with various systemic autoimmune diseases. Since the marginal zone is considered to be the splenic lodging site of this B cell subset and since increases of ED3+ macrophages have been associated with autoimmune diseases in the rat, the observed changes of the marginal zones in HCB-treated rats is in line with this notion.