Abstract
Immunoprotective function of oligodeoxynucleotides containing CpG motifs (CpG-ODN) has been demonstrated in neonatal chickens against common bacterial pathogens such as E.coli and Salmonella sp. Our recent study reported that CpG-ODN administration enriches immune compartments in neonatal chicks. However, a causal relationship between CpG-ODN-induced immune enrichment and protective mechanisms remains unestablished. In this study, we investigated in ovo administered CpG-ODN-mediated immune cell recruitment in the immunological niches in lymphoid (spleen) and nonlymphoid (lungs) organs using various doses of CpG-ODN and examined whether the immunological profiles have any correlation with immunoprotection against E.coli infection. Eighteen-day-old embryonated eggs were injected with either 5, 10, 25, and 50 μg of CpG-ODN or saline (n = ~40 per group). On the day of hatch (72 hr after CpG-ODN treatment), we collected the spleen and lungs (n = 3‐4 per group) and examined the recruitment of macrophages/monocytes, their expression of MHCII and CD40, and the number of CD4+ and CD8+ T-cell subsets in the immunological niches in the spleen and lungs using flow cytometry. We observed the dose-dependent recruitment of immune cells, wherein 25 μg and 50 μg of CpG-ODN induced significant enrichment of immunological niches in both the spleen and the lungs. Four days after the CpG-ODN treatment (1-day after hatch), chicks were challenged with a virulent strain of E. coli (1 × 104 or 1 × 105 cfu, subcutaneously). Clinical outcome and mortality were monitored for 8 days postchallenge. We found that both 25 μg and 50 μg of CpG-ODN provided significant protection and reduced clinical scores compared to saline controls against E. coli infection. Overall, the present study revealed that CpG-ODNs orchestrate immunological niches in neonatal chickens in a dose-dependent manner that resulted in differential protection against E. coli infection, thus supporting a cause and effect relationship between CpG-ODN-induced immune enrichment and the antibacterial immunity.
Highlights
Infectious diseases of neonatal poultry are common due to the immaturity of the immune system or inadequate sensitization of the immune system to antigens [1]
The groups that received 25 μg or 50 μg of Oligodeoxynucleotides containing CpG motifs (CpG-ODN) per bird showed a significant increase in the lung antigen-presenting cells (APCs) population compared to the saline control group (~3 and ~4 times higher, respectively) (Figures 1(a) and 1(b))
The highest APC percentage was seen with 50 μg of CpG-ODN and lowest with the saline control
Summary
Infectious diseases of neonatal poultry are common due to the immaturity of the immune system or inadequate sensitization of the immune system to antigens [1]. Antimicrobials are effective in controlling bacterial diseases, and the prophylactic use of antimicrobials is a common practice in the poultry industry [4]. These prophylactic use of antibiotics in the poultry industry may lead to antibiotic residues in poultry products [5, 6] and the emergence of antibiotic-resistant strains of bacteria [4, 7]. Since the use of category antibiotics has been discontinued since 2014 [8], the poultry industry needs suitable alternatives to antibiotics for controlling diseases in neonatal chickens [9, 10]
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