p. injection was
assessed in adult zebrafish. The fish were treated with NLc liposomes, empty liposomes, the mixture of free immunostimulants (poly(I:C) and LPS) or PBS. At 7 days post-injection, all the fish were subjected to an immersion challenge with SVCV ( Fig. 4). Similarly to the bacterial challenge neither the empty liposomes nor the mixture of free immunostimulants offered any significant protection relative to the control fish, as measured at 15 days (RPS of empty liposomes: 0%; free immunostimulants: 7.7%). Only the fish that had received NLc liposomes showed a significantly higher survival rate (RPS of 42.3% after 15 days) ( Fig. 4 and supplementary Table 1). This difference was evident throughout the entire experiment. We Fluorouracil manufacturer also evaluated the biodistribution of fluorescently labelled NLc liposomes (AF750-NLc liposomes) in zebrafish following administration by immersion. The zebrafish were treated by placing them into water tanks containing AF750-NLc liposomes. At 0 h, fluorescence was detected GW-572016 price in the gills of all fish and by 12 h post-immersion, fluorescence was still detected in the gills but was also detected in the abdominal region of most of the fish (83.3%) (Fig. 5A). To accurately gauge the organ distribution of the NLc liposomes, ex vivo
imaging was performed at 12 h post-immersion ( Fig. 5B). Fluorescence was observed in the gills of all fish (100%), and in the intestine and the liver of some fish (83.3% and 50% of fish, respectively). Thus, the results suggest that the NLc liposomes had attached to the gill surface, and that they had reached the liver and the intestine. We cannot discard that NLc liposomes also reached the intestine by the fish having swallowed water during immersion . Having confirmed that these liposomes can be administered by immersion, we then evaluated their efficacy by the latter route against SVCV immersion challenge. In this case, the empty liposomes and the mixture of free immunostimulants gave a slight increase in the survival at 13 days: RPS was 20.0% with empty liposomes, 21.4% with free poly(I:C)/LPS
(Fig. 6 and supplementary Table 1). However, the only statistically significant difference in the entire survival curve was observed in the NLc liposome-treated fish, whose mortality was clearly delayed throughout the experiment (RPS value of 33.3%) (Fig. 6 Vasopressin Receptor and supplementary Table 1). Our experiments on NLc liposomes administered to adult zebrafish by i.p. injection clearly indicated that the spleen was the main organ in which the liposomes had accumulated. This finding is consistent with the fact that the spleen is amongst the most important organs for filtering out foreign agents  and is the main organ for antigen presentation in teleost fish . Furthermore, this result is in agreement with those of previous studies, in which the uptake and retention of injected bacteria, vaccine antigens and liposomes were demonstrated in the spleen and the head kidney  and .