HgCl2-induced human lymphocyte activation in vitro: A superantigenic mechanism?

Mercuric chloride (HgCl2) has been proposed to be a mitogen for human blood lymphocytes in vitro. In our previous study, we demonstrated that HgCl2 pr eferentially stimulates the CD4+ T cell subset to blast transformation and DNA synthesis and that the reaction is dependent on CD14+ accessory cells. In order to characterise the responding cells further and to elucidate the mechanism of T cell activation, the T cell receptor (TCR) V beta chain expr ession of the blast-transformed cells was analysed by monoclonal antibodies and flow cytometry. The 22 TCR-V beta-specific antibodies used were found to react with 55-80% of the naive CD4+ and CD8+ blood T cells from the diff erent donors. Six to 18% of the lymphocytes, mainly CD4+ T cells, were blas t transformed after addition of HgCl2. The distribution of the lymphoblasts carrying certain TCR VB chains were skewed, and 15-40% expressed the TCR V beta 2 chain. Furthermore, if cells were pretreated for 5 days with HgCl2, whereafter recombinant interleukin-2 in fresh medium was added, the TCR V beta 7+ T cell subset was also stimulated to blast transformation. The supe rantigen staphyloccal enterotoxin B, as a control, induced blast transforma tion in 10-26% of the lymphocytes, mainly CD4+ T cells, which were, as expe cted, positive for V beta 3, V beta 12, V beta 14 or V beta 17. We conclude that HgCl2 has characteristics of a superantigen, activating the human lym phocytes in a V beta-chain-selective manner in vitro.