Molecular mechanisms behind the temporal dynamics of LPS-induced inflammatory response in splenic phagocytes of the wall lizard Hemidactylus flaviviridis.

Our understanding of the molecular mechanisms underlying the reptilian immune response is strikingly limited despite their significant evolutionary placement between ectothermic anamniotes and endothermic amniotes. Hence, the current study attempted to understand the time kinetics of inflammatory pathways activated in immunostimulated splenic phagocytes of the wall lizard Hemidactylus flaviviridis. Our in vitro study revealed increased phagocytosis in splenic phagocytes at all time points (2, 8 and 12 h) of lipopolysaccharide (LPS) treatment. Further, qPCR analysis revealed LPS-induced modulation of immune-relevant genes in lizard splenic phagocytes. A biphasic increase in tlr4 mRNA was observed at 2 h and 12 h of LPS treatment along with increased tlr2 at all durations. Furthermore, in the early hours of LPS treatment, the expression of a signalling molecule (myd88) and transcription factors (nfκb and ap1) was upregulated. In addition, splenic phagocytes cultured with LPS for 2 h demonstrated increased expression of the pro-inflammatory cytokine il1β and antioxidant enzyme catalase genes with an inhibition of the anti-inflammatory cytokine tgfβ gene. While the heightened il1β and catalase expression reached basal levels 8 h post-LPS treatment, tgfβ expression returned to basal levels only after 12 h. Further, the current study also examined the expression of arginase, a marker of cell repair, which was significantly higher than respective controls at all time durations of LPS treatment. However, its maximal expression at 12 h is suggestive of increased cell repair activity during extended infection. Our results indicate activation of a pro-inflammatory and anti-oxidant response during the early hours of LPS exposure in splenic phagocytes, which dampens during later hours of bacterial challenge, raising the possibility of a shift to an anti-inflammatory and reparative response.