ZnO nanoparticles induced adjuvant effect via toll-like receptors and Src signaling in Balb/c mice.

Our previous studies indicated that zinc oxide nanoparticles (ZnO NPs) have adjuvant properties to a known allergen ovalbumin (OVA) in Balb/c mice. Therefore, in this study, we focused on the mechanisms involved in adjuvant responses induced by ZnO NPs. The eosinophil counts in the Peyers' patches of intestine and ICAM-1, Cox2 protein expressions were enhanced in the ZnO NPs/OVA group. Following screening of toll-like receptors (TLRs), TLR 2, 4 and 6 were found to be increased. Accordingly, we found that downstream proteins of TLRs such as myeloid differentiation primary response protein-88 (MyD88), IL-1 receptor associated kinase 1 (IRAK 1), and TNFR-associated factor 6 (TRAF 6) were also found to be enhanced in the ZnO NPs/OVA-induced group. These inflammatory responses underlined the critical roles of TLRs in the inflammatory response. ZnO NPs increased the mRNA levels of inflammatory cytokine IL-1β and protein expression of several mediators, including Cox2, PGE2, MMP-9 and finally caspase 1 in macrophages. Another pathway for adjuvant effect is Src which was found to be significantly affected by the activation of p-Lyn, p-Syk, IP3, p-PLC-γ and cAMP. Ca(2+) influx was significantly increased as well in the ZnO NPs/OVA group. These findings demonstrated the differential role of TLRs in regulation of the ZnO NPs-induced adjuvant responses causing the inflammation. We therefore, conclude that ZnO NPs have significant adjuvant effect via following Src kinase and TLRs signaling that ascribed to inflammatory responses due to recruitment and activation of adhesion molecules and inflammatory cells. The adjuvant property of ZnO NPs may help in planning strategies for its therapeutic use.