Interplay between extracellular -SH groups and Ca2+ in their mitogenic action on murine lymphocytes: the role of SiO2

Murine spleen lymphocytes, cultured under serum-free conditions and stimulated with concanavalin A (Con A), showed an increased demand for supplemental concentrations of Ca2+ when 2-mercaptoethanol (2-ME) or L-cysteine were also present in the culture medium. The requirement for additional Ca2+ ions was particularly evident at high cell concentrations. The addition of SiO2 (Aerosil 200), in concentrations depending on the original level of Ca2+ in the culture medium, could substitute for the increased demand on calcium ions. This dependency of SiO2 effects on calcium levels in the medium was also evident when supraoptimal, i.e. inhibitory concentrations of silica were tested. Results of experiments with 45Ca suggest that silica particles may act as intercellular carriers of calcium. In contrast to spleen lymphocytes, Con A-stimulated thymus cells exhibited neither a need for an increase in the concentration of Ca2+ nor a dependency on the presence of 2-ME in the medium.