| As new members of carbon material family, carbon nanotubes (CNTs) have become the subject of intense investigation because of their unique structural, electrical and mechanical properties. They have a wide range of promising applications in drug delivery, therapy and biomedical imaging. However, a crucial step toward the application of CNTs in human body is to regulate their impacts on immune systems.CNTs (both single and multiwalled CNTs) have been reported to cause perturbations of the immune system in vitro and in vivo. Such adverse effects severely limit the applications of CNTs in biomedicine. Although there have been reports on CNT's perturbations on cellular signaling events such as NFκB and AP-1, the associated mechanism is not understood. Even more critical is the complete lack of strategy to remediate immunotoxicity of CNTs and other nanomaterials targeted for biomedical applications. We wanted to find the upstream mechanisms of NFκB pathway activation of CNTs and the strategy to modulate CNTs'immunotoxicity.We previously designed and synthesized an 80-member combinatorial MWCNTs library by placing most diverse molecules on the nanotubes surface. Based on the screening of this library for the immune responses, MWCNT 1 and 2 were classified as the two extreme groups separately and selected for the following investigations. MWCNT 2 exhibited reduced immune perturbations in macrophages through multiple assays, such as cell viability, NO production, TNF-α, ROS gengration and cell function. Therefore we wanted to know how MWCNTs affected macrophages and modulated their immunotoxicity.We demonstrated the uptake presses of MWCNTs by macrophages. Alougth both of MWCNTs had the same uptake amount and distributed in identical cellular location, the recognication of them by macrophages surface receptors were defferent. Internalization of MWNCT 1 was inhibited similarly by both mannose receptor and scanvenger receptor inhibitors, while MWCNT 2 was inhibited mainly by scanvenger receptor inhibitor. The results indicated that MWCNT 1 could be recognized by mannose receptor and scanvenger receptor similarly, while MWCNT 2 could be preferred recognized by scanvenger receptor rather than mannose receptor. Then, NFκB pathway activation of macrophages treated with MWCNTs was assayed. The activation of NFκB elicited by MWCNT 2 was much lower than MWCNT 1. Phagocytosis of NPs via mannose receptor-mediated pathways results in a variety of downstream events, including reactive oxygen intermediates, cytokines such as IL-1, IL-6, TNF-a, and NFκB activation. Nevertheless, scanvenger receptor-mediated uptake is not accompanied by pro-inflammatory cytokines secretion and NFκB activation. The results illustrated that the chemistry modification on MWCNT 2 surface evidently alleviated the activation of the NFκB pathway which were related to the preferred recognization and uptake by scanvenger receptor.We further assessed the effect of MWCNTs on immune systems in mice. After tail v.ein injection, MWCNTs were mostly accumulated in lungs, liver and spleen in 24 hrs. TNF-αand IL-1βin the tissue homogenates of mouse lungs, liver and spleen 24 hrs after injection were quantified. MWCNT 1 elicited an elevated response of cytokines in lung and liver, which were obviously defferent from MWCNT 2 treatment. MWCNT 2 did not induce evident immune response as measured by these cytokines. After detected the activation of NFκB pathway by Western blot, we found that MWCNT 2 did not promote the NFκB activation as high as MWCNT 1. These results confirmed that the chemistry modification on MWCNT 2 surface evidently alleviated the activation of the NFκB pathway and thus reduced their immunetoxicity in mice.In summary, we demonstrated that the surface chemistry modification on MWCNTs can regulates the immune perturbation in mice and in macrophages. MWCNT 2 caused less immune perturbations compared to MWCNT 1 both in mice and in macrophages. The mechanistic explanation is that the chemistry modification on MWCNT 2 surface increased its binding to scavenger receptor. The recognition by scavenger receptor alleviated NFκB activation and reduced immunotoxicity of MWCNT 2. The elucidation of immunotixicity of nanomaterials are exemplifies here and, more importantly, we establish an approach to modify nanomaterials to reduce their immune perturbations will facilitate the wide applications of nanomaterials in medicane and life sciences.
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