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 reptilian immune response is strikingly limited despite their significant evolutionary placement between ectothermic anamniotes and endothermic amniotes. Hence, the current study attempts to understand time kinetics of inflammatory pathway activated in immunostimulated splenic phagocytes of wall lizard, Hemidactylus flaviviridis. Our in vitro study revealed increased phagocytosis in splenic phagocytes at all time points (2, 8, and 12h) of LPS treatment. Further, qRT-PCR analyses revealed LPS-induced modulation of immune-relevant genes in lizard splenic phagocytes. A biphasic increase in tlr4 mRNA was observed at 2h and 12h of LPS treatment along with increased tlr2 at all durations. Furthermore, early hours of LPS treatment upregulated the expression of signalling molecules (myd88 and trif) and transcription factors (nfκb and ap1). Also, 2h LPS treatment stimulated the expression of pro-inflammatory cytokine, il1β and antioxidant enzyme, catalase with an inhibition of the anti-inflammatory cytokine, tgfβ. While the heightened il1β and catalase reached basal levels 8h post LPS treatment, tgfβ returned to basal levels only after 12h. 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 12h is suggestive of increased cell repair activity during extended infection. Our results indicate activation of a pro-inflammatory and anti-oxidant response during 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.