Vaccination against the Protozoan Parasite Histomonas meleagridis Primes the Activation of Toll-like Receptors in Turkeys and Chickens Determined by a Set of Newly Developed Multiplex RT-qPCRs.

Taniya Mitra,Beatrice Bramberger,Dieter Liebhart,Ivana Bilic,Michael Hess

doi:10.3390/vaccines9090960

Abstract

Histomonosis in turkeys and chickens is caused by the extracellular parasite Histomonas meleagridis, but the outcome of the disease varies depending on the host species. So far, studies on the immune response against histomonosis focus mainly on different traits of the adaptive immune system. Activation of toll like receptors (TLR) leads to the interplay between cells of innate and adaptive immunity with consequences on B and T cell clonal expansion. Therefore, the present investigation focused on the interaction of virulent and/or attenuated histomonads with the innate immune system of turkeys and chickens at 4, 10, 21 days post inoculation. The expression of TLRs (TLR1A, 1B, 2A, 2B, 3, 4, 5, 6(Tu), 7, 13(Tu) and 21(Ch)) and pro-inflammatory cytokines (IL1β and IL6) were analysed in caecum and spleen samples by RT-qPCR. Most frequent significant changes in expression levels of TLRs were observed in the caecum following infection with virulent parasites, an effect noticed to a lower degree in tissue samples from birds vaccinated with attenuated parasites. TLR1B, 2B and 4 showed a continuous up-regulation in the caecum of both species during infection or vaccination, followed by challenge with virulent parasites. Vaccinated birds of both species showed a significant earlier change in TLR expression following challenge than birds kept non-vaccinated but challenged. Expression of TLRs and pro-inflammatory cytokines were associated with severe inflammation of diseased birds in the local organ caecum. In the spleen, changes in TLRs and pro-inflammatory cytokines were less prominent and mainly observed in turkey samples. In conclusion, a detailed comparison of TLRs and pro-inflammatory cytokines of the innate immune system following inoculation with attenuated and/or virulent H. meleagridis of two avian host species provides an insight into regulative mechanisms of TLRs in the development of protection and limitation of the disease.

Highlights

Due to the fatality of the disease in infected turkeys no data is available from this species at 21 days post inoculation (DPI)
The present work revealed for the first time the innate immune response in poultry by measuring toll like receptors (TLR) expression against H. meleagridis, an extracellular protozoan parasite
The present data confirm that the timely expression of TLRs might contribute towards the immune protection of turkeys and chickens against H. meleagridis

Summary

Introduction

Histomonas meleagridis is a widespread flagellated parasite of poultry which causes histomonosis Blackhead disease, histomoniasis or infectious typhlohepatitis) [1]. Histomonosis can be fatal, resulting in typhlohepatitis with severe pathological lesions characterized by an acute inflammation of caecum and liver. The disease is less destructive, but can cause similar lesions in both organs, with consequences on performance [2]. Experimental vaccination with in-vitro attenuated parasites was shown to be effective in turkeys and chickens against a challenge and might be used in the future to protect birds [4]. Knowledge of the immune response of poultry against the parasite is limited and mainly focused on the adaptive immunity [5]. No studies have been performed investigating the innate immune response against H. meleagridis, especially toll-like receptors (TLRs), together with pro-inflammatory cytokines expression

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