Translocation of intratracheally instilled multiwall carbon nanotubes to lung-associated lymph nodes in rats

In order to assess the extrapulmonary effects of multiwall carbon nanotubes (MWCNT), deposition of MWCNT and histopathologic changes in lung-associated lymph nodes (LALN) were examined in MWCNT-administered rats. At the age of 13 wk, male F344 rats were intratracheally instilled with MWCNT at a dose of 0 (vehicle), 40 or 160 μg/rat. The rats were sacrificed on Day 1, 7, 28 or 91 after instillation and light microscopic examinations were performed on LALN tissues. MWCNT was translocated to right and left posterior mediastinal lymph nodes and parathymic lymph nodes. Deposition of MWCNT was greater in the posterior mediastinal lymph node than in the parathymic lymph node, and the amount of MWCNT deposited in these two lymph nodes increased gradually and dose-dependently with time. MWCNT was phagocytosed by nodal macrophages, and some of the MWCNT-laden macrophages were aggregated. Transmission electron microscopic (TEM) observation confirmed the presence of MWCNT fibers with a characteristic multi-walled cylindrical structure.