ENHANCED T-LYMPHOCYTE EXPRESSION OF LFA-1, ICAM-1, AND THE TNF RECEPTOR FAMILY MEMBER OX40 IN HGCL2-INDUCED SYSTEMIC AUTOIMMUNITY

Injection of mercuric chloride into Brown Norway (BN) rats induces a T lymphocyte-dependent autoimmune syndrome. In order to investigate whe ther modification of adhesion and costimulatory molecules on T lymphoc ytes may be involved in early T lymphocyte activation by HgCl2, the au thors analysed expression of these molecules in peripheral lymph node cells from BN rats at day 4 after injection of HgCl2. Tri-colour flow cytometry was performed for expression analysis within CD45RC-defined subsets of CD4(+) and CD8(+) cells. Compared to control rats, HgCl2-ex posed rats showed increased numbers of lymphocytes, especially of T ly mphocyte blast cells. The levels of LFA-1 expression as well as the fr actions of ICAM-1(+) cells were significantly increased in all CD45RC- defined subsets of CD4(+) and CD8(+) cells. Within the CD4(+)CD45RC(lo ) T lymphocyte population, HgCl2-injected rats showed a highly signifi cant increase in the number of cells expressing OX40, which is a membe r of the TNF receptor family. Moreover, only CD4(+) CD45RC(lo) blast c ells of HgCl2-exposed rats showed decreased expression of CD43, increa sed expression of CD49d and decreased numbers of CD26 (+) cells. The r esults indicate that induction of autoimmunity by HgCl2 in BN rats is associated with altered expression of T lymphocyte costimulatory molec ules, predominantly on CD4(+) CD45RC(lo) cells, which may be caused by a direct effect of HgCl2 on these cells, and may precipitate further activation of T and B lymphocytes by HgCl2.