Abstract
Koala Retrovirus (KoRV) has been widely speculated to cause immune suppression in koalas (Phascolarctos cinereus) and to underlie the koala’s susceptibility to infectious disease, however evidence for immunomodulation is limited. The aim of this study is to determine whether immunophenotypic changes are associated with KoRV infection in free ranging Victorian koalas. qPCR was used to examine mRNA expression for Th1 (IFNγ), Th2-promoting (IL6, IL10) and Th17 (IL17A) cytokines, along with CD4 and CD8 in whole blood of koalas (n = 74) from Mt Eccles and Raymond Island in Victoria, Australia, with and without natural chlamydial infection. KoRV positive koalas had significantly lower levels of IL17A (p`0.023) and IFNγ (p = 0.044) gene expression along with a decreased CD4:CD8 gene expression ratio (p = 0.025) compared to negative koalas. No effect of chlamydial infection or combined effect of KoRV and chlamydial infection was detected in these populations. The decreased expression of IFNγ could make KoRV infected koalas more susceptible to persistent chlamydial infection, and a decrease in IL17A could make them more susceptible to gram negative bacterial, fungal and mycobacterial infection; but more tolerant of chlamydial infection.
Highlights
Koala Retrovirus (KoRV) is a gamma retrovirus that has been widely speculated to cause immune suppression in koalas (Phascolarctos cinereus) and to underlie the koala’s susceptibility to infectious disease
We examine resting IFNγ, Interleukin 6 (IL6), Interleukin 10 (IL10) and IL17A, CD4 and CD8 mRNA expression in koalas in two populations in Victoria (Mt Eccles and Raymond Island), in which KoRV A and Chlamydia pecorum infect koalas
Reference gene cytokine mRNA levels could be quantified in 74 samples and, of those, IL17A mRNA was quantifiable in 68 samples, IL10 in 61, IFNγ in 55, IL6 in 52, CD4 in 42, CD8 in 51 and CD4:CD8 in 39
Summary
Koala Retrovirus (KoRV) is a gamma retrovirus that has been widely speculated to cause immune suppression in koalas (Phascolarctos cinereus) and to underlie the koala’s susceptibility to infectious disease. Experimental evidence for an effect of KoRV A on the immune system is limited to a single study in which human peripheral blood mononuclear cells (PBMC’s) incubated with KoRV A increased expression of the Th2 associated cytokines Interleukin 6 (IL6) and Interleukin 10 (IL10)[8]. KoRV does contain several structural elements that are associated with immune suppression by closely related gamma retroviruses such as FeLV and Murine Leukaemia Virus (MuLV) These include the viral transmembrane protein p15E5, which is associated with a multitude of immune suppressive effects including inhibition of lymphocyte activation by mitogens and modulation of cytokine expression by peripheral blood mononuclear cells (PBMC’s)[5]. Population wide studies in humans are limited, researchers have consistently found that IL10 promoting polymorphisms are associated with increased ocular scarring and infertility in people with ocular and genital chlamydial infections[17,18]
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