Polyclonal human T-cell activation by silicate in vitro

Silica (SiO₂) or related substances such as silicone ([-R₂Si-O-](n)), which is used in plastic surgery, or asbestos (e.g. chrysotile; 3MgO·2SiO₂·H₂O) have 'adjuvant effects'. In a study of scleroderma patients in Germany more than 78% had experienced exposure to silicate dust. T-cell receptor (TcR) Vβ gene analysis on CD4^- CD8^- double-negative αβ T cells from scleroderma patients, using polymerase chain reaction (PCR), showed that certain Vβ genes, Vβ5, Vβ7 and Vβ17, were predominantly expressed in the cells. We found that certain Vβ repertoires, Vβ5.3 and Vβ6.7, were predominantly expressed on fractionated T cells with a high Ca²⁺ level that had been stimulated by chrysotile in vitro. The intracellular Ca²⁺ level in human peripheral blood mononuclear cells (PBMC) increased after incubation with silica or chrysotile. Interleukin-2 (IL-2) release from PMBC also rose significantly with chrysotile stimulation, but no change was observed when major histocompatibility complex (MHC) class II DP/DR positive cells were depleted. Therefore, our results support the possibility that silicate acts as a superantigen.