The Effect of Innate Immune Receptor Activation on Differential Breed Responses to LPS in Sheep.

Abstract While studying breed differences in immune response of peripheral blood mononuclear cells (PBMC) to Haemonchus contortus (Hc) antigen, RNA sequencing revealed that St. Croix (STC) PBMC upregulated expression of NLRP3 compared to PBMC from Suffolk (SUF) sheep. Nod-like receptor pyrin containing domain 3 (NLRP3) is a cytoplasmic pattern recognition receptor (PRR) with a wide array of agonists, such as PAMPs, DAMPs, ATP, bacterial product, and viral products. Stimulation of the NLRP3 inflammasome results in proteolytic activation of IL-1b and IL-18, cell pyroptosis, and classically, the induction of proinflammatory responses. Common activation of this pathway can be achieved by stimulation with liposaccharide (LPS) which binds and activates a toll-like receptor-4 (TLR4) pathway, causing production of proinflammatory cytokines. Interestingly, NLRP3 has been recently implicated as an early initiator of IL-4 production in response to helminth antigen. Thus, the objective of this study was to determine differences in breed responses to LPS and the role of NLRP3. To test this hypothesis, PBMC were collected from STC and SUF sheep and cells were incubated with LPS only, LPS in combination with pharmacological inhibitor of NLRP3 (MCC950), or complete media for 3 hrs. Gene expression of PBMC exposed to LPS revealed that Inflammatory linked genes IL-1β (P < 0.001), TLR4 (P < 0.001), TNFα (P < 0.001), NFκB (P < 0.001) were upregulated in STC PBMC. Treatment with MCC950 in combination with LPS, reduced inflammatory gene expression in STC PBMC to the level of SUF PBMC (P > 0.05), thus ablating inflammatory responses in STC PBMC. These data reveal a deficiency in NLPR3 function in SUF sheep and have been confirmed by SNPs found in that gene that have been predicted to alter NLRP3 protein structure.