Identification of Rat Quantitative Trait Loci that Regulate LPS‐Induced Pro‐Inflammatory Cytokine Responses

Abstract

Bacterial lipopolysaccharides (LPSs) trigger innate immune effector functions, such as the production of pro‐inflammatory cytokines. Here we utilized major histocompatibility complex (MHC)‐congenic rats to dissect the genetic basis of strain‐dependent variations of LPS‐induced tumour necrosis factor‐α (TNF‐α) levels in a whole blood in vitro assay. PVG.1AV1 background was associated with a high response, ACI background with a medium response, and LEW.1AV1 and DA backgrounds were associated with low responses. To determine the location of regulating non‐MHC genes, a genome‐wide linkage analysis with 236 microsatellite markers was performed on 186 F2 progeny of high TNF‐α responder PVG.1AV1 and MHC identical but low TNF‐α responder LEW.1AV1 rats. A region on rat chromosome 1 displayed linkage to LPS‐induced TNF‐α responses (P = 3.3 × 10−5). In addition, a locus on chromosome 2 was linked to responses of both interleukin‐6 (IL‐6) (P = 2.3 × 10−5) and TNF‐α (possible linkage, P = 8 × 10−3). Both chromosome regions have been linked to inflammatory diseases in rats, and so have the homologous regions in mice and humans. We therefore suggest that continued genetic dissection of the described in vitro phenotypes will give clues to both normal physiological regulation of LPS‐induced TNF‐α production and disease pathways.

RGMA and IL21R show association with experimental inflammation and multiple sclerosis

“…Higher TNF and IL-6 levels were driven by the susceptible dark Agouti (DA) alleles at the distal QTL, whereas higher IL-6 levels were driven by the resistant PVG.1AV1 alleles at the proximal QTL. The G 12 AIL thus confirmed and considerably refined previously reported linkage 26 and provided evidence for at least two distinct genes that regulate levels of TNF and IL-6.…”

“…26 To confirm and refine this region, peripheral blood from 465 rats of the twelfth generation (G 12 ) of an AIL was stimulated with LPS and screened for TNF and IL-6 production. The linkage analysis defined two distinct loci regulating IL-6 production, whereas TNF production only linked to the distal locus ( Figure 1a).…”

“…Stimulation with LPS was then performed as reported previously. 26 Supernatants from whole blood stimulations were collected after 18 h and stored at À70 1C. Protein quantifications for TNF and IL-6 were performed using ELISA.…”

“…25 In this study, we investigate a quantitative trait locus on rat chromosome 1, originally identified in a (LEW.1AV1  PVG.1AV1) F 2 cross (Lewis  Piebald-ViralGlaxo), which carries variants of gene(s) regulating levels of tumor necrosis factor (TNF), interleukin (IL)-6 and IL1b. 26 Interestingly, the QTL overlaps loci that regulate EAE and PIA. 27,28 Defining genes behind this region might therefore unravel genetically controlled pathways that regulate inflammation in general.…”

The Arthritis Severity Quantitative Trait Loci Cia4 and Cia6 Regulate Neutrophil Migration into Inflammatory Sites and Levels of TNF-α and Nitric Oxide

“…To our knowledge this is the first description of a non-MHC arthritis locus, Cia4, which regulates levels of TNF-␣ in a synovial-like cavity, thus making it even more relevant to disease. One previous study implicated non-MHC loci on rat chromosomes 1 and 2 in the regulation of serum levels of TNF-␣ in response to LPS in a different intercross (41). TNF-␣ is a key mediator in the pathogenesis of rheumatoid arthritis and experimental models of arthritis in rodents.…”