Studying avian immune response to an intermediate strain of IBDV

JUAN MANUEL CARBALLEDA; SILVINA CHIMENO ZOTH; EVANGELINA GÓMEZ; MARÍA J. GRAVISACO; A. BERINSTEIN

Congreso; XI Avian Immunology Research Grupo Meeting; 2010

Infectious Bursal Disesase (IBD) is a highly contagious, wide spread immunosuppressive chicken disease caused by the Infectious Bursal Disease Virus (IBDV).  IBDV is a two segmented double-strand RNA virus, member of the Birnaviridae family.          In order to study the interaction between IBDV and the immune system, chickens were exposed to an intermediate IBDV strain by both, intramuscular and oral routes, and sacrificed at 1, 3, 5 and 28 days post inoculation (DPI). Using Real Time PCR we analyzed the expression of a panel of avian cytokines and chemokines in duodenum, spleen and Bursa of Fabricius. Also, splenic nitric oxide (NO) production and immunocompromised cellular populations were analyzed by Griess reaction and flow cytometry, respectively.           Intramuscular IBDV inoculation promoted an over expression of proinflamatory cytokines as IL-6, IL-15 and gINF in spleen, which correlated with an increase of gINF plasma concentration measured by ELISA. At 3DPI, gIFN expression was still up-regulated in spleen. At 5DPI, an over expression of IL-15 was observed in the bursa. Splenic NO production was measured in supernatants of splenocytes stimulated (or not) with Concanavalin A (ConA). Intramuscular inoculation of IBDV caused an increment of NO concentration in supernatants at 1DPI. At 3 and 5DPI, no increase of NO was detected in splenocytes from IBDV when compared with PBS treated animals. In addition, at 3 and 5 DPI splenocytes of chickens inoculated with IBDV appeared to be insensitive to ConA stimulation.          When IBDV was orally administered, plasma concentration of gIFN was strongly increased at 3DPI compared with control animals. Flow cytometry analysis of the bursa showed a strong T- lymphocyte infiltration and a decrease in B- lymphocyte populations in animals inoculated with IBDV at 5DPI. The Adherent/no Adherent splenic cells ratio displayed an increment of adherent (macrophages) cells in the spleen at 1DPI but no differences were detected at 3DPI in IBDV inoculated animals. At 5DPI, splenocytes of IBDV treated chickens showed a lower Ad. / Non Ad. ratio, suggesting a drop in macrophage population of the spleen. Splenic NO production was higher in IBDV inoculated chickens only at 1DPI.                              In summary, results obtained in the present work showed that IBDV of intermediate virulence induced similar effects as previously described for highly virulent IBDV, in terms of up regulation of inflammatory cytokines expression in spleen and bursa, early increase of spleen macrophages with augmented NO production followed by a significant decrease in the number of these cells, and  infiltration of T lymphocytes in the bursa, among others. These results allow us to be confident in the study of the immune response against IBDV using non virulent virus as a model.