After amputation, granular hemocytes infiltrate the blastema of regenerating cephalic tentacles of the freshwater snail Pomacea canaliculata. Here, the circulating phagocytic hemocytes were chemically depleted by injecting the snails with clodronate liposomes, and the effects on the cephalic tentacle regeneration onset and on Pc-Hemocyanin, Pc-transglutaminase (Pc-TG) and Pc-Allograft Inflammatory Factor-1 (Pc-AIF-1) gene expressions were investigated. Flow cytometry analysis demonstrated that clodronate liposomes targeted large circulating hemocytes, resulting in a transient decrease in their number. Corresponding with the phagocyte depletion, tentacle regeneration onset was halted, and it resumed at the expected pace when clodronate liposome effects were no longer visible. In addition to the regeneration progress, the expressions of Pc-Hemocyanin, Pc-TG, and Pc-AIF-1, which are markers of hemocyte-mediated functions like oxygen transport and immunity, clotting, and inflammation, were modified. After the injection of clodronate liposomes, a specific computer-assisted image analysis protocol still evidenced the presence of granular hemocytes in the tentacle blastema. This is consistent with reports indicating the large and agranular hemocyte population as the most represented among the professional phagocytes of P. canaliculata and with the hypothesis that different hemocyte morphologies could exert diverse biological functions, as it has been observed in other invertebrates.

The increasing fragmentation of plastic debris into nanosized particles represents a threat to freshwater ecosystems, yet the biological effects of nanoplastics (NPs) on freshwater invertebrates remain poorly understood. This study investigated tissue distribution, cellular effects and immune responses following acute exposure to polyethylene terephthalate nanoplastics (PET-NPs) in the freshwater gastropod Pomacea canaliculata, a species of high ecological relevance and physiological resilience. Adult snails were injected with PET-NPs at 5 or 10 mg/L and sampled after 24 and 72 h. PET-NPs accumulation in the anterior and posterior kidneys was assessed by fluorescence imaging and tissue morphology was evaluated. Stress- and inflammation-related genes (Pc-Heat Shock Protein (HSP)70, Pc-HSP90 and Pc-Allograft inflammatory factor 1) expression was quantified by RT-qPCR. PET-NPs uptake and phagocytic activity were analyzed in circulating hemocytes in vivo and ex vivo. PET-NPs were accumulated in renal tissues, persisting up to 72 h without histopathological alterations. Gene expression analyses revealed non-linear and dose/time-dependent responses. Hemocytes of different morphologies internalized PET-NPs in a dose-dependent manner and showed intercellular particle transfer. Overall, acute PET-NP exposure determines rapid immune handling and tissue sequestration with limited short-term physiological impact, underscoring the potential involvement of immune processes in NPs fate and highlighting the need for chronic exposure studies.

In vertebrates, circulating and tissue-resident immune cells contribute to host defense and tissue homeostasis. Their balance is maintained through hematopoiesis and anatomical reservoirs. In mollusks, this balancing is poorly investigated. Thus, the dynamics of circulating and tissue-resident hemocytes after a hemolymph withdrawal were analyzed in Pomacea canaliculata, a snail that allows repeated hemolymph withdrawals and possesses posterior kidney (PK) cell aggregates known as hemocyte islets. In the absence of specific hemocyte markers, flow cytometry data revealed dynamic changes in circulating hemocyte number and populations within 48 h following hemolymph withdrawal. In addition, computer-assisted image analysis of histological sections showed a significant transient reduction in PK hemocyte-islet area. Analyses of publicly available P. canaliculata transcriptomes revealed predominant and highly variable expression of two hematopoiesis-related genes, namely Transglutaminase (PcTGase) and Hematopoietically expressed homeobox protein (PcHhex), in circulating hemocytes and PK. Fluorescence in situ hybridization highlighted constitutive PcTGase and PcHhex expression within PK hemocyte islets. RT-qPCR experiments confirmed transcriptomic data on PcTGase and PcHhex constitutive expression, without significant modulation following hemolymph withdrawal. Collectively, these findings provide the first evidence of parallel recovery dynamics involving circulating hemocytes and PK hemocyte islets in P. canaliculata.