Treatment with a maximum dose of 6?mg/kg body weight was well tolerated by the animals. However, both for 20?nm and 100?nm Ag-NP growth retardation was observed during the treatment. A severe increase in spleen size and weight was present which was due to an increased cell number. Both T and B cell populations showed an increase in absolute cell number, whereas the relative cell numbers remained constant. At histopathological evaluation brown and black pigment indicating Ag-NP accumulation was noted in spleen, liver, and lymph nodes. Ag-NP was also detected incidentally in other organs. Clinical chemistry indicated liver damage (increased alkaline phosphatase, alanine transaminase, and aspartate transaminase) that could not be confirmed by histopathology. Hematology showed a decrease in several red blood cell parameters.
The most striking toxic effect was the almost complete suppression of the natural killer (NK) cell activity in the spleen at high doses. Other immune parameters affected were: decreased interferon-¦Ã and interleukin (IL)-10 production by concanavalin-A stimulated spleen cells, increased IL-1¦Â and decreased IL-6, IL-10 and TNF-¦Á production by lipopolysaccharide stimulated spleen cells, increase in serum IgM and IgE, and increase in blood neutrophilic granulocytes. For the spleen weight a critical effect dose of 0.37?mg/kg body weight (b.w.) could be established. The lowest critical effect dose (CED) for a 5 % change compared to control animals was observed for thymus weight (CED05 0.01?mg/kg b.w.) and for functional immune parameters, i.e. decrease in NK cell activity (CED05 0.06?mg/kg b.w.) and LPS stimulation of spleen cells (CED05 0.04?mg/kg b.w.). These results show that for nanosilver the most sensitive parameters for potential adverse responses were effects on the immune system.