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BACKGROUND:Lymph-targeted tracing and therapy based on carbon nanotubes have been one of the hottest researches on targeting tumor diagnosis and treatment. To evaluate the accumulation of carbon nanotubes in axil ary lymph node can provide experimental evidences for developing nano-tracers and drug carriers which are more lymph-specific and more biocompatible. OBJECTIVE:To study the accumulation of the intravenously injected carboxylated single-wal ed carbon nanotubes in axil ary lymph nodes of Sprague-Dawley rats, and to evaluate their effect on blood cel s. METHODS:Sixty-four Sprague-Dawley rats were randomly divided into two groups. Rats in testing group were injected with carboxylated single-wal ed carbon nanotubes suspension (2 mg/kg), while those in control group were injected with 5%glucose solution (1 mL/kg), both through the tail vein, three times per week. Four periods of 7, 60, 90 and 120 days were set (the 120-day period referred to 90 days of administration fol owed by 30 days of drug withdrawal). At the end of each period, eight rats from each group were randomly picked out, to col ect blood samples via the abdominal aorta for blood routine test. Final y the axil ary lymph nodes were observed, and the lymph node samples of rats in the testing group were col ected and analyzed at 120 days by transmission electron microscope. RESULTS AND CONCLUSION:Compared with the control group, black staining of axil ary lymph nodes of rats in testing group was not obvious at the end of the 7-day period. However, with the increase of the dosing periods, the lymph nodes of the rats in the testing group became enlarged, firm and black stained, coupled with a significant rising in the percentage of blood neutrophils. After 30 days of drug withdrawal, the size of the rat axil ary lymph nodes was reduced and black staining partly faded, with the decreasing of blood neutrophil percentage. Under the transmission electron microscope, abundant carboxylated single-wal ed carbon nanotubes were uptaken by lymphocytes to form a large number of phagocytic vacuoles after drug withdrawal for 30 days. It indicates that the short-term tracing of rat axil ary lymph nodes by carboxylated single-wal ed carbon nanotubes injected through the tail vein is relatively weak, while the long-term intravenous injection can cause their accumulation in rat axil ary lymph nodes, coupled with the increase of neutrophils;after drug withdrawal, the carboxylated single-wal ed carbon nanotubes can be slowly cleared by the lymph nodes.