Silver is commonly used both in ionic form and in nanoparticulate form as a bactericidal agent. This is generally ascribed to a higher toxicity towards prokaryotic cells than towards mammalian cells. Comparative studies with both silver ions (such as silver acetate) and polyvinylpyrrolidone (PVP)-stabilized silver nanoparticles (70 nm) showed that the toxic effect of silver occurs in a similar concentration range for Escherichia coli, Staphylococcus aureus, human mesenchymal stem cells (hMSCs), and peripheral blood mononuclear cells (PBMCs), i.e. 0.5 to 5 ppm for silver ions and 12.5 to 50 ppm for silver nanoparticles. For a better comparison, bacteria were cultivated both in Lysogeny broth medium (LB) and in Roswell Park Memorial Institute medium (RPMI)/10% fetal calf serum (FCS) medium, as the state of silver ions and silver nanoparticles may be different due to the presence of salts, and biomolecules like proteins. The effective toxic concentration of silver towards bacteria and human cells is almost the same.

Spherical gold nanoparticles with a hydrodynamic diameter between 25 and 37 nm were prepared and stabilised with poly(N-vinylpyrrolidone) (PVP) or tris(sodium-m-sulfonatophenyl)phosphine (TPPTS). They were subjected to different cell culture media, e.g. pure RPMI, RPMI containing up to 10% of fetal calf serum (FCS), and RPMI containing up to 10% of bovine serum albumin (BSA), and the rate of agglomeration was studied by dynamic light scattering. In pure RPMI, a strong agglomeration was observed whereas in the RPMI–FCS and RPMI–BSA mixtures the particles remained well dispersed above 1 wt% protein concentration. The effect of PVP-stabilised gold nanoparticles on human mesenchymal stem cells (hMSC) was studied as well. No significant influence on the viability and chemotaxis was observed after incubation of hMSC with gold nanoparticles. However, gold nanoparticles induced the activation of hMSC as indicated by the release of IL-6 and IL-8.

AFTER SEVERE injuries, dysbalanced cytokine synthesis contributes to dysregulated immune functions and to enhanced susceptibility toward microbial infections. During the past decade, the pattern of helper T cells type 1 (T_H1) and type 2 (T_H2) has been recognized as a fundamental principle of T-cell responses.¹ Helper T cells type 1 are potent producers of interleukin 2 (IL-2) and interferon γ (IFN-γ); in contrast, T_H2 cells produce IL-4, IL-5, or IL-13.² Intracellular staining of cytokine generation in activated T cells has emerged as a powerful tool to discriminate T_H1 and T_H2 cells using flow cytometry.² Recently, several studies^3-6 have described distinct alterations in the T_H1-T_H2 ratio of peripheral lymphocytes obtained from severely burned and surgical patients. Whereas after severe burn trauma a clear increase in T_H2 cells but no decrease in T_H1 cells has been reported,^5,6 different observations were made in surgical patients. No increase in T_H2 cells but a significant decrease in T_H1 cells has been observed after conventional hernia repair.³ An increased or unaltered release of IL-4 has been reported^7,8 from isolated lymphocytes after conventional cholecystectomy, accompanied by a decrease in the release of IL-2 or IFN-γ, respectively. In addition, it was shown⁹ that cytokine release from T_H1 and T_H2 cells was concomitantly diminished in severely injured patients with trauma. Furthermore, in vivo exposure of healthy individuals to endotoxin led to reduced production of T_H1 cytokines but not to an increase in T_H2 cytokines from stimulated whole blood.¹⁰ Because of similar conflicting results obtained in animal trauma models,^11-13 the effect of severe injuries on the T_H1/T_H2 pattern remains unclear.

For a comparative cytotoxicity study, nanoparticles of the noble metals Rh, Pd, Ag, Pt, and Au (spherical, average diameter 4 to 8 nm) were prepared by reduction in water and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Thus, their shape, size, and surface functionalization were all the same. Size and morphology of the nanoparticles were determined by dynamic light scattering (DLS), analytical disc centrifugation (differential centrifugal sedimentation, DCS), and high-resolution transmission electron microscopy (HRTEM). Cell-biological experiments were performed to determine the effect of particle exposure on the viability of human mesenchymal stem cells (hMSCs). Except for silver, no adverse effect of any of the metal nanoparticles was observed for concentrations up to 50 ppm (50 mg L⁻¹) incubated for 24 h, indicating that noble metal nanoparticles (rhodium, palladium, platinum, gold) that do not release ions are not cytotoxic under these conditions.