J Vet Sci.  2022 Mar;23(2):e27. 10.4142/jvs.21225.

Expression of Toll-like receptors 3, 7, 9 and cytokines in feline infectious peritonitis virus-infected CRFK cells and feline peripheral monocytes

• Khair MHMM
• Selvarajah GT
• Omar AR
• Mustaffa-Kamal F

• KMID: 2527882
• DOI: http://doi.org/10.4142/jvs.21225

Abstract

Background
The role of Toll-like receptors (TLRs) in a feline infectious peritonitis virus (FIPV) infection is not completely understood.
Objectives
This study examined the expression of TLR3, TLR7, TLR9, tumor necrosis factoralpha (TNF-α), interferon (IFN)-β, and interleukin (IL)-10 upon an FIPV infection in CrandellReese feline kidney (CRFK) cells and feline monocytes.
Methods
CRFK cells and monocytes from feline coronavirus (FCoV)-seronegative cats and FCoV-seropositive cats were infected with type II FIPV-79-1146. At four, 12, and 24 hours postinfection (hpi), the expression of TLR3, TLR7, TLR9, TNF-α, IFN-β, and IL-10, and the viral load were measured using reverse transcription quantitative polymerase chain reaction. Viral protein production was confirmed using immunofluorescence.
Results
FIPV-infected CRFK showed the upregulation of TLR9, TNF-α, and IFN-β expression between 4 and 24 hpi. Uninfected monocytes from FCoV-seropositive cats showed lower TLR3 and TLR9 expression but higher TLR7 expression compared to uninfected monocytes from FCoV-seronegative cats. FIPV-infected monocytes from FCoV-seropositive cats downregulated TLR7 and TNF-α expression between 4 and 24 hpi, and 4 and 12 hpi, respectively. IFN-β was upregulated early in FIPV-infected monocytes from FCoV-seropositive cats, with a significant difference observed at 12 hpi compared to FCoV-seronegative cats. The viral load in the CRFK and FIPV-infected monocytes in both cohorts of cats was similar over time.ConclusionTLR7 may be the key TLR involved in evading the innate response against inhibiting TNF-α production. Distinct TLR expression profiles between FCoVseronegative and FCoV-seropositive cats were observed. The associated TLR that plays a role in the induction of IFN-β needs to be explored further.

Keyword

Feline infectious peritonitis (FIP); Toll-like receptor (TLR); cytokine; monocytes