Tissue-specific mRNA expression profiles of porcine Toll-like receptors at different ages in germ-free and conventional pigs

Abstract

Toll-like receptors (TLRs), key initiators of innate immune responses, recognize antigens and are essential in linking innate and adaptive immune responses. Misrecognition and over-stimulation/expression of TLRs may contribute to the development of chronic inflammatory diseases and autoimmune diseases. However, appropriate and mature TLR responses are associated with the establishment of resistance against some infectious diseases. In this study, we assessed the mRNA expression profile of TLRs 1-10 in splenic and ileal mononuclear cells (MNCs) and dendritic cells (DCs) of germ-free (GF) and conventional pigs at different ages. We found that the TLR mRNA expression profiles were distinct between GF and conventional pigs. The expression profiles were also significantly different between splenic and ileal MNCs/DCs. Comparison of the TLR expression profiles in GF and conventional newborn and young pigs demonstrated that exposure to commensal microbiota may play a more important role than age in TLR mRNA expression profiles. To our knowledge, this is the first report that systematically assesses porcine TLRs 1-10 mRNA expression profiles in MNCs and DCs from GF and conventional pigs at different ages. These results further highlighted that the commensal microbiota of neonates play a critical role through TLR signaling in the development of systemic and mucosal immune systems.

Keywords: Microbiota; Toll-like receptor; mRNA expression.

Figure 1. TLRs 1-10 mRNA expression profiles in newborn pigs

(A) The expression profiles in splenic MNCs of newborn pigs; (B) The expression profile in splenic and ileal MNCs of conventional newborn pigs. Bars represent SD, different letters indicate significant difference (p < 0.05). GF: germ-free; Conv: conventional. (n=4)

Figure 2. TLRs 1-10 mRNA expression profiles in germ-free and conventional young pigs

(A) The expression profiles in splenic MNCs of young pigs; (B) The expression profiles in ileal MNCs of young pigs; (C) The expression profiles in splenic and ileal MNCs of young germ-free pigs; (D) The expression profiles in splenic and ileal MNCs of young conventional pigs. Bars represent SD, different letters indicate significant difference (p < 0.05). Gn: germ-free; Conv: conventional. (n=4)

Figure 3. TLRs 1-10 mRNA expression profiles in MNCs and DCs of conventional adult pigs

(A) The expression profiles in MNCs of conventional adult pigs; (B) The expression profiles in DCs of conventional adult pigs. Bars represent SD, different letters indicate significant difference (p < 0.05). (n=4)

Figure 4. TLRs 1-10 mRNA expression profiles in splenic and ileal MNCs of conventional pigs at different ages

(A) TLR1; (B) TLR2; (C) TLR3; (D) TLR4; (E) TLR5; (F) TLR6; (G) TLR7; (H) TLR8; (I) TLR9; (J) TLR10 expression profiles in conventional pigs at different ages. Bars represent SD. * p < 0.05; ** p < 0.01; *** p < 0.001. (n=4)

Figure 5. TLRs 1-10 mRNA expression profiles in DCs of young pigs

(A) The expression profiles in ileal DCs of young pigs; (B) The expression profiles in splenic and ileal DCs of conventional young pigs. Bars with same letter in each TLR are not significant difference (p > 0.05). Bars represent SD and bars with different letters in each TLR are significant difference (p < 0.05). (n=4)

Figure 6. TLRs mRNA expression profiles in splenic and ileal DCs of conventional pigs at different ages

(A) TLR1 expression profile in splenic DCs; (B) TLR2 expression profile in splenic DCs; (C) TLR3 expression profile in splenic DCs; (D) TLR8 expression profile in splenic DCs; (E) TLR2 expression profile in ileal DCs; (F) TLR 6 expression profile in ileal DCs; (G) TLR9 expression profile in ileal DCs; (H) TLR4 expression profile in ileal DCs. Bars represent SD. The significant differences between two groups were indicated with star(s). * p < 0.05; ** p < 0.01. (n=4)