Correlation between cytokine profile, antibody titre and viral load during sub-clinical chicken anaemia virus infection.

Th e present work was carried out to investigate the correlation between viral load and the cytokine pro- fi le and virus specifi c antibody levels at fi ve day intervals up to 25 days post infection (dpi) in various tissues of chicks infected with chicken infectious anaemia virus (CIAV) at six weeks of age (sub-clinical infection). For determining the viral load in the various tissues, recombinant plasmid VP2-pET32b was prepared and serially diluted tenfold for the generation of a standard curve using real time polymerase chain reaction (PCR). Cytokine fold changes in mRNA levels of IFN-γ, IL-1, IL-2, IL-12 in the spleen and IFN-γ, IL-12 in freshly collected whole blood were determined. Th e results showed that peak viral load occurs between 10-20 days post infection in the lymphoid tissues viz., thymus, spleen, liver, bone marrow, bursa and also blood, being highest in blood followed by thymus. A varied response in the expression levels of individual cytokines was observed during all the intervals post infection. Th e IFN-γ increased two to fi ve fold in blood and spleen while IL-2 decreased in the splenic tissue during the same period. Peak IFN-γ coincided with peak viral load in the spleen at 10 dpi while in blood it peaked earlier at fi ve days post infection and remained high during the peak viral load at 10-20 dpi. Virus specifi c antibodies were signifi cantly higher at 15 dpi and were thereafter found to be strongly associated with viral load regression although higher concentrations of virus remained in the blood and thymic tissues until 25 dpi, indicating a role of other immune components in virus clearance. In conclusion, this study reports a negative correlation of viral load and the progression of the antibody response and IFN-γ cytokine expression in chicks infected with CIAV during their sub-clinical infectious stage. However, cytokine expression from the various individual immune cells like monocytes, heterophils, CD4 + T, CD8 + T cells and others during the pathogenesis of this immunosuppre ssive poultry pathogen remains to be elucidated.