Toll-Like Receptor Expression Profiles in Koala (Phascolarctos cinereus) Peripheral Blood Mononuclear Cells Infected with Multiple KoRV Subtypes

Abstract

Toll-like receptors (TLRs), evolutionarily conserved pattern recognition receptors, play an important role in innate immunity by recognizing microbial pathogen-associated molecular patterns. Koala retrovirus (KoRV), a major koala pathogen, exists in both endogenous (KoRV-A) and exogenous forms (KoRV-B to J). However, the expression profile of TLRs in koalas infected with KoRV-A and other subtypes is yet to characterize. Here, we investigated TLR expression profiles in koalas with a range of subtype infection profiles (KoRV-A only vs. KoRV-A with KoRV-B and/or -C). To this end, we cloned partial sequences for TLRs (TLR2–10 and TLR13), developed real-time PCR assays, and determined TLRs mRNA expression patterns in koala PBMCs and/or tissues. All the reported TLRs for koala were expressed in PBMCs, and variations in TLR expression were observed in koalas infected with exogenous subtypes (KoRV-B and KoRV-C) compared to the endogenous subtype (KoRV-A) only, which indicates the implications of TLRs in KoRV infection. TLRs were also found to be differentially expressed in koala tissues. This is the first report of TLR expression profiles in koala, which provides insights into koala’s immune response to KoRV infection that could be utilized for the future exploitation of TLR modulators in the maintenance of koala health.

Toll-Like Receptor and Cytokine Responses to Infection with Endogenous and Exogenous Koala Retrovirus, and Vaccination as a Control Strategy

“…Moreover, whether these have significant downstream effects on signaling pathways in koalas is yet to be characterized. Differential expression of TLRs were also observed in tissues obtained from two koalas [77]. However, the phenotype of TLR expression also needs to be investigated in KoRV-negative and KoRV-positive koalas with multiple KoRV subtypes from a range of habitats and disease states in order to gain further insights into the future exploitation of TLR modulators [78].…”

“…Recently, we characterized TLR expression patterns in koala PBMCs, and observed that all of the reported TLRs (TLR2-10 and TLR13 mRNA) were expressed in PBMCs [77]. The expression of TLR4-7 and TLR10 were upregulated (Figure 1A) in koalas infected with endogenous KoRV-A and exogenous KoRV-B and KoRV-C, compared to KoRV-A-only infected koalas, and TLR7, TLR8, and TLR10 expressions were also upregulated (Figure 1B) in koalas infected with endogenous KoRV-A and exogenous KoRV-C, compared to KoRV-A-only infected koalas, which may imply the role of TLRs in KoRV infection [77]. However, this study was limited by sample size, where ten koalas were used in the absence of any KoRV-negative koalas.…”

“…However, the phenotype of TLR expression also needs to be investigated in KoRV-negative and KoRV-positive koalas with multiple KoRV subtypes from a range of habitats and disease states in order to gain further insights into the future exploitation of TLR modulators [78]. [77]). When compared with KoRV-A-infected koalas, upregulation was observed in TLR4-TLR7, and TLR10 mRNA in KoRV-A, KoRV-B, and KoRV-C-infected koala peripheral blood mononuclear cells (PBMCs) (A), and TLR7, TLR8, and TLR10 mRNA in KoRV-A and KoRV-C-infected koala PBMCs (B).…”

“…The first evidence for the immunomodulatory effects of KoRV was obtained by the increased expression of interleukin-6 (IL-6), IL-10, growth-related oncogene and monocyte chemotactic protein-1 upon the exposure of KoRV to human PBMCs [40]. However, the advances of CD4, CD8, and [77]). When compared with KoRV-A-infected koalas, upregulation was observed in TLR4-TLR7, and TLR10 mRNA in KoRV-A, KoRV-B, and KoRV-C-infected koala peripheral blood mononuclear cells (PBMCs) (A), and TLR7, TLR8, and TLR10 mRNA in KoRV-A and KoRV-C-infected koala PBMCs (B).…”

“…Figure 1. TLR response to infection with multiple KoRV subtypes in koalas (summarized from[77]). When compared with KoRV-A-infected koalas, upregulation was observed in TLR4-TLR7, and TLR10 mRNA in KoRV-A, KoRV-B, and KoRV-C-infected koala peripheral blood mononuclear cells (PBMCs) (A), and TLR7, TLR8, and TLR10 mRNA in KoRV-A and KoRV-C-infected koala PBMCs (B).…”