Background: Titanium dioxide (TiO 2 ) is well known component of sun creams and cosmetics. Human and environmental exposure to TiO 2 powder producing a potential systemic health effects including interference with the immune response need to be considered.

Aim: The aim of this study was to evaluate the effects of TiO 2 nanoparticles on natural and acquired immune response using in vitro human peripheral blood model. Method: Human peripheral whole blood cultures were treated with TiO 2 (15-60nm) NPs in three different concentrations: 0.12, 3 and 75 μg/cm 2 for 4h, 24h, 48h and 72h. Phagocytic activity of granulocytes and monocytes, respiratory burst of phagocytes, natural killer cell activity and proliferative activity of lymphocytes were used to assess the effect of NPs on immune cell functions.

Results: No cytotoxic effect of TiO 2 NPs to human blood cells up to concentration of 75 μg/cm 2 (106 μg/ml) was found. No suppressive effect of NPs of phagocytic activity of monocytes was found. Opposite stimulatory effect on phagocytic activity of granulocytes treated with low dose (LD) and middle dose (MD) of TiO 2 for 24h and respiratory burst (MD, 24h) was observed. Similarly, significant enhancement of natural killer cell activity in cells exposed to MD of TiO 2 NPs for 24h was shown. Examination of proliferative activity of lymphocytes found significant stimulation of lymphocytes treated with high dose (HD) of TiO 2 NPs for last 4h of 72h cultivation period. T-lymphocyte proliferative response and T- dependent B-cell response in vitro in cell cultures stimulated with phytohemagglutinin, concanavalin A and pokeweed mitogens were significantly increased after 4h exposure to HD of TiO 2 NPs. Proliferative response of T-lymphocytes through the T-cell receptor (CD3 antigen) was different – significant suppression without clear dose-dependence was observed.

Conclusions: Our findings might indicate stimulatory effect of TiO 2 NPs on human blood cells, particularly granulocytes and natural killer cells. Different response of B-lymphocytes and T- cell subpopulations to NPs was observed.