Differential expression of T-cell adhesion molecules and LFA-1-dependent intercellular adhesion in HgCl2-induced autoimmunity and immune suppression

Exposure of Brown Norway (BN) rats to HgCl2 induces Th2-mediated systemic autoimmunity. In contrast, in Lewis rats, HgCl2 induces immune suppression, mediated by CD8(+) T cells. HgCl2 was previously found to enhance expression of LFA-1, ICAM-1 and CD134 (OX40) on T cells in BN rats. In the present study, T cells from Lewis rats were studied at day 4 after injection of HgCl2. CD8(+) T lymphoblasts were significantly increased, which were predominantly CD45RC(hi), and which showed enhanced LFA-1 expression. Furthermore, CD4(+)CD45RC(hi) T cells showed increased numbers of ICAM-1(+) cells, whereas expression of CD134 and CD26 was relatively decreased in CD4(+) T lymphoblasts. Ex vivo experiments demonstrated that HgCl2-exposure of BN rats, but not of Lewis rats, significantly enhances PMA [phorbol 12-myristate 13-acetate]-induced lymphocyte aggregation, mediated by LFA-1 and ICAM-1. In conclusion, HgCl2-injected Lewis rats show early signs of T-lymphocyte activation, predominantly on CD8(+) cells. Strain-dependent effects of HgCl2 on cell adhesion molecules and expression of CD134 may play an important role in development of either autoimmunity or immune suppression.