Noble metal nanoparticles, especially silver due to its antimicrobial properties, are amongst the most widely used types of nanomaterials, and so the possibility of an organism’s exposure to them is relatively high. Excluding injections, there are three natural routes they can accidentally enter the body – the skin, lungs and the alimentary tract. Research on rodents indicate that after inhalation, injection or oral administration silver, gold and copper nanoparticles can easily enter the systemic circulation and reach the internal organs. Particularly vulnerable to the harmful effects of nanoparticles are organs with an extended reticuloendothelial system, such as the spleen, where the accumulation of nanoparticles occurs. It is well proved that metallic nanoparticles are easily absorbed by macrophages located in lymphoid tissues but cannot be destroyed inside the cells. They remain unchanged in phagosomes and chronically stimulate the cells to pro-inflammatory cytokine production. They can also interact with other cell types present in the local environment, e.g. lymphocytes, which can lead to an inadequate immunological response of the organism. Many authors have described the pro-inflammatory effect of noble metal nanoparticles, both local to the application site and generalized. What is more, silver nanoparticles were able to disturb the Th1/Th2 balance or even cause an allergic response of the organism. The beneficial impact of silver nanoparticles on the immune response occurs only when they were applied externally in the form of dressings or ointments in the treatment of wounded or inflamed skin. In such cases nanosilver exhibited immunoregulatory properties accelerating the healing. An explanation for this mode of action may be the fact of relatively poor skin penetration by nanoparticles, limiting their effect to the local tissues only.
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