BackgroundThe pathogenesis of immunological tolerance caused by avian leukosis virus subgroup J (ALV-J), an oncogenic retrovirus, is largely unknown.ResultsIn this study, the development, differentiation, and immunological capability of B cells and their progenitors infected with ALV-J were studied both morphologically and functionally by using a model of ALV-J congenital infection. Compared with posthatch infection, congenital infection of ALV-J resulted in severe immunological tolerance, which was identified as the absence of detectable specific antivirus antibodies. In congenitally infected chickens, immune organs, particularly the bursa of Fabricius, were poorly developed. Moreover, IgM-and IgG-positive cells and total immunoglobulin levels were significantly decreased in these chickens. Large numbers of bursa follicles with no differentiation into cortex and medulla indicated that B cell development was arrested at the early stage. Flow cytometry analysis further confirmed that ALV-J blocked the differentiation of CD117+chB6+ B cell progenitors in the bursa of Fabricius. Furthermore, both the humoral immunity and the immunological capability of B cells and their progenitors were significantly suppressed, as assessed by (a) the antibody titres against sheep red blood cells and the Marek’s disease virus attenuated serotype 1 vaccine; (b) the proliferative response of B cells against thymus-independent antigen lipopolysaccharide (LPS) in the spleen germinal centres; and (c) the capacities for proliferation, differentiation and immunoglobulin gene class-switch recombination of B cell progenitors in response to LPS and interleukin-4(IL-4) in vitro.ConclusionsThese findings suggested that the anergy of B cells in congenitally infected chickens is caused by the developmental arrest and dysfunction of B cell progenitors, which is an important factor for the immunological tolerance induced by ALV-J.

BackgroundCo-infection with avian leukosis virus subgroup J and reticuloendotheliosis virus induces synergistic pathogenic effects and increases mortality. However, the role of exosomal miRNAs in the molecular mechanism of the synergistic infection of the two viruses remains unknown.ResultsIn this study, exosomal RNAs from CEF cells infected with ALV-J, REV or both at the optimal synergistic infection time were analysed by Illumina RNA deep sequencing. A total of 54 (23 upregulated and 31 downregulated) and 16 (7 upregulated and 9 downregulated) miRNAs were identified by comparing co-infection with two viruses, single-infected ALV-J and REV, respectively. Moreover, five key miRNAs, including miR-184-3p, miR-146a-3p, miR-146a-5p, miR-3538 and miR-155, were validated in both exosomes and CEF cells by qRT-PCR. GO annotation and KEGG pathway analysis of the miRNA target genes showed that the five differentially expressed miRNAs participated in virus-vector interaction, oxidative phosphorylation, energy metabolism and cell growth.ConclusionsWe demonstrated that REV and ALV-J synergistically increased the accumulation of exosomal miRNAs, which sheds light on the synergistic molecular mechanism of ALV-J and REV.Electronic supplementary materialThe online version of this article (10.1186/s12977-018-0427-0) contains supplementary material, which is available to authorized users.

Avian leukosis virus subgroup J (ALV‐J) was isolated in meat‐type breeder chickens for the first time in 1988 in the United Kingdom. Due to the application of an eradication program, there were fewer reports related to myelocytomatosis or ALV‐J in China after 2013. However, there was another breakout almost simultaneously in six provinces of China in February 2018. On‐site, 15‐ to 20‐week‐old broiler breeder chickens showed depression, paralysis and weight loss. Mortality for certain flocks reached 15%. Sick chickens showed numerous yellow–white neoplasms growing in the sternum, rib and lumbar vertebra and had hepatic and renal metastasis. Histopathological observation showed all neoplasms were myelocytomas, and there were massive myelocyte‐like tumour cells in the liver, kidney and bone marrow. To explore the aetiology of this re‐outbreak of myelocytomatosis in China, we collected tumour‐bearing chickens and isolated six strains of ALV‐J (GM0209‐1 to ‐6). Phylogenetic analysis of gp85 and gp37 showed GM0209 strains were clearly distinct from the prototype strain of ADOL‐7501, HPRS‐103 and NX0101, and there was a mutation, R176G, in the conserved region between hr1 and hr2 regions of gp85, which was not found in other 44 ALV‐J strains. The 3′UTR nucleotide sequences of GM0209 isolates showed there was a signature deletion of 11 nt that was also present in 3′UTR sequences of SCDY1 and NHH, two isolates that have a reported association with haemangioma, indicating this deletion could not determine the tumour type induced by ALV‐J. Although the eradication program of ALV‐J has been successfully applied in China, the outbreak of ALV‐J still occurred, and the virus strain spread quickly. Thus, the biocharacteristics and pathogenesis of mutational ALV‐J should be further studied.

Macrococcus caseolyticus is generally considered to be a non-pathogenic bacterium that does not cause human or animal diseases. However, recently, a strain of M. caseolyticus (SDLY strain) that causes high mortality rates was isolated from commercial broiler chickens in China. The main pathological changes caused by SDLY included caseous exudation in cranial cavities, inflammatory infiltration, haemorrhages and multifocal necrosis in various organs. The whole genome of the SDLY strain was sequenced and was compared with that of the non-pathogenic JCSC5402 strain of M. caseolyticus. The results showed that the SDLY strain harboured a large quantity of mutations, antibiotic resistance genes and numerous insertions and deletions of virulence genes. In particular, among the inserted genes, there is a cluster of eight connected genes associated with the synthesis of capsular polysaccharide. This cluster encodes a transferase and capsular polysaccharide synthase, promotes the formation of capsules and causes changes in pathogenicity. Electron microscopy revealed a distinct capsule surrounding the SDLY strain. The pathogenicity test showed that the SDLY strain could cause significant clinical symptoms and pathological changes in both SPF chickens and mice. In addition, these clinical symptoms and pathological changes were the same as those observed in field cases. Furthermore, the anti-microbial susceptibility test demonstrated that the SDLY strain exhibits multiple-antibiotic resistance. The emergence of pathogenic M. caseolyticus indicates that more attention should be paid to the effects of this micro-organism on both poultry and public health.

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