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.

No abstract

Congenital avian leukosis virus subgroup J (ALV-J) infection can induce persistent immunotolerance in chicken, however, the underlying mechanism remains unclear. Here, we demonstrate that congenital ALV-J infection induces the production of high-frequency and activated CD4+CD25+ Tregs that maintain persistent immunotolerance. A model of congenital infection by ALV-J was established in fertilized eggs, and hatched chicks showed persistent immunotolerance characterized by persistent viremia, immune organ dysplasia, severe imbalance of the ratio of CD4+/CD8+ T cells in blood and immune organs, and significant decrease in CD3+ T cells and Bu-1+ B cells in the spleen. Concurrently, the mRNA levels of IL-2, IL-10, and IFN-γ showed significant fluctuations in immune organs. Moreover, the frequency of CD4+CD25+ Tregs in blood and immune organs significantly increased, and the frequency of CD4+CD25+ Tregs was positively correlated with changes in ALV-J load in immune organs. Interestingly, CD4+CD25+ Tregs increased in the marginal zone of splenic nodules in ALV-J-infected chickens and dispersed to the germinal center. In addition, the proliferation and activation of B cells in splenic nodules was inhibited, and the number of IgM+ and IgG+ cells in the marginal zone significantly decreased. We further found that the mRNA levels of TGF- β and CTLA-4 in CD4+CD25+ Tregs of ALV-J-infected chickens significantly increased. Together, high-frequency and activated CD4+CD25+ Tregs inhibited B cells functions by expressing the inhibitory cytokine TGF-β and inhibitory surface receptor CTLA-4, thereby maintaining persistent immunotolerance in congenital ALV-J-infected chickens.

No abstract

Background: Immune tolerance induced by retrovirus is a prerequisite for tumorigeness. We had reported that B-cell anergy was the main reason for immune tolerance induced by avian leukosis virus subgroup J (ALV-J). However, the molecular mechanism remains unclear. Results: Initially, we found that Lyn showed down-regulation in chick embryo fibroblasts (CEF) and up-regulation in B-cells infected by ALV-J. So, we speculated that tyrosine kinase Lyn plays a key role in B-cell anergy induced by ALV-J. Confocal laser scanning microscopy (CLSM) and co-immunoprecipitation (Co-IP) results demonstrated that ALV-J indirectly regulated the expression of Lyn. To further investigate the role and regulatory mechanism of Lyn in B-cell anergy induced by ALV-J, the expression levels of Lyn and Syk at different phosphorylation site, the Ca 2+ mobilization, and the expression levels of NF-κB p65 protein in vitro and vivo were detected in B-cells. The result showed that Ca 2+ mobilization was delayed and p65 expression level was decreased in B-cells after ALV-J infection. Consistently, the retrieve of Ca 2+ mobilization, expression levels of NF-κB p65 were found after RNA interference of Lyn. Subsequently, we demonstrated that the activation of phosphorylated Lyn protein at Tyr507 site played a critical role in B-cells anergy, which were verified by the fact of the significantly up-regulation of the expression levels of phosphorylated Syk protein at Tyr525/526 site when RNA interference for Lyn were performed in B-cells. Furthermore, immunohistochemical (IHC) staining results confirmed that the expression levels of Lyn phosphorylated protein at Tyr507 site in bursal cells were increased, while the expression levels of Syk phosphorylated protein at Tyr525/526 sites were decreased. Conclusions: These findings suggested that Lyn inhibited BCR signal pathway mediates B-cell anergy under ALV-J infection，which will provide a new insight for revealing the molecular mechanism of immune tolerance induced by ALV-J. Keywords: avian leukosis virus subgroup J , B-cell anergy, immune tolerance, Lyn, Syk