Abstract

The present study was designed to study cytokine profile and lymphocytic proliferation activity in chicken infectious anaemia virus (CIAV) infected chicks at various intervals of clinically susceptible age. Briefly, ninety specific pathogen free (SPF) chicks were divided into five experimental groups (A to E). Groups A to D were inoculated with 0.5 ml of 10^4.5TCID₅₀ of CIAV intramuscularly at 1, 14, 21 and 28-day-old, respectively, while group E served as uninfected control. Comparative cytokine gene expression levels of interleukin (IL)-1β, IL-10, IL-12β and granulocyte macrophage-colony stimulating factor (GM-CSF) were measured at 4 and 7 days post infection (dpi) by qRT-PCR. Also, lymphocytic proliferation activity was measured at 1, 2 and 3 week post infection (wpi) by lymphocyte transformation test (LTT). The down regulatory changes in cytokines and depressed cell mediated immune (CMI) responses were observed in chicks of all infected groups (A to D), which were significantly (p<0.05) low as compared to control group. Higher intensities and more pronounced effects on cytokine downregulation and blastogenic responses of lymphocytes were seen at younger ages. Apoptosis in thymic DNA as detected by nucleosomal fragmentation was highest on 7 and 10 dpi and lowest on 14 dpi, which correlated with down regulated cytokine profile in all infected groups. The development of clinical signs and lesions along with PCR testing confirmed the establishment of CIAV infection in experimental chicks. Increased apoptosis, decreased PCV, depletion of lymphocytes, down regulated cytokine profile and reduced lymphocyte activity explain involvement of thymic and hematopoietic precursor cells leading to CMI suppression caused by CIAV. Altogether, immunopathological changes were more severe in chicks infected at younger ages as compared to later ages of the clinically susceptible period.However, further studies are suggested regarding the impact of viral load on the various cytokine profiles and revealing more about immunopathogenesis of CIAV both in young and adult birds.

Key words: Chicken infectious anemia virus, cell mediated immune response, polymerase chain reaction (PCR), qRT-PCR, cytokine, apoptosis.