Lymphocyte activation by liposome-trapped streptozotocin in murine popliteal lymph node (PLN) test

Abstract

The lymphoproliferative potential of liposome-trapped streptozotocin (STZ) was compared to the effect of saline-dissolved STZ injected locally into the foot pad of CD-1 mice. Popliteal lymph node (PLN) enlargement and early cell activation of lymphocyte subsets were monitored during the onset of STZ-induced autoimmune-like reaction. Injection of the optimal STZ dose, 0.5 mg/foot pad, markedly increased the absolute PLN cell number as well as specific T-helper (CD4 +), T-suppressor/cytotoxic (CD8 +), and B-(Ig +) cell subsets stained with fluorescent monoclonal antibodies. Furthermore, there was a marked increase in the number of large/activated CD4 + and CD8 + cells and subsets bearing specific markers of early activation. These included cells stained with fluorescein-conjugated monoclonal antibodies against interleukin-2 receptor (CD25 +) and early activation marker (EAM +) (CD69 +), and with fluorescein-conjugated peanut agglutinin (PNS +). Surprisingly, the injection of liposome-trapped STZ, at a 1 10 of the optimal dose only, induced a marked PLN enlargement comparable to the effect of optimal STZ dose. The effect of liposome-STZ could be dissociated from the non-drug-containing MLV-related lymphocyte activation. The data suggest several possible advantages from the introduction of chemicals by the liposome route and the subsequent PLN test for chemical-induced autoimmunity. Toxicological advantages could involve better control of chemical exposure, controlled exposure to the water-insoluble substances, drastic reduction of xenobiotic dose, a stronger, clear PLN response and possible elimination or at least restriction of false-negative results, due to the liposome adjuvancity. Overall, application of liposomes as an exposure route potentialized the STZ-induced early lymphocyte activation.