The autoimmunogenic chemicals HgCl2 and diphenylhydantoin stimulate IgG production to TNP–Ficoll and TNP–OVA, supporting and extending the graft‐versus‐host hypothesis for chemical induction of autoimmunity

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Abstract
Bypass of T-cell tolerance via non-cognate graft-versus-host (GVH)-like help from T-helper (Th) cells activated by chemically altered or induced epitopes, has been postulated as a mechanism underlying chemical induction of autoimmunity. To functionally test this hypothesis, we assessed whether the autoimmunogenic chemicals HgCl2 and diphenylhydantoin (DPH), like GVH reactions, stimulate specific immunoglobulin G (IgG) responses to trinitrophenyl (TNP)-Ficoll but not to TNP-ovalbumin. IgG responses were quantified in the popliteal lymph node by enzyme-linked immunosorbent spot-forming cell assay (ELISPOT) assays 7 days after s.c. injection of antigens, parental cells, chemicals or combinations thereof into the footpad of semi-allogeneic F1 mice. Antigens, chemicals, or cells alone induced few TNP-specific IgG antibody-forming cell (AFC) compared with untreated mice. Co-injection of parental cells or chemicals with TNP-Ficoll stimulated the TNP-specific response per lymph node approximately 50- and approximately 40-fold, respectively. In contrast, the IgG response to TNP-ovalbumin could not be stimulated by GVH reactions, whereas HgCl2 and DPH dose-dependently increased this response up to approximately 25- and approximately 250-fold, respectively. However, responses to TNP-ovalbumin pre-incubated with HgCl2 or DPH could be stimulated approximately 6-8 fold by GVH reactions. Observed similar adjuvanticity of chemicals and parental cells for TNP-Ficoll support a GVH-like action of autoimmunogenic chemicals. In addition, the chemicals modify TNP-ovalbumin such that B cells recognizing this antigen become susceptible to non-cognate stimulation by GVH reactions.