Effects of age on immune function in broiler chickens

Abstract

Background: There are many diseases in poultry, many of which are caused by poor immune function. It is not clear how cytokines and various immune cell functions change with age in modern broilers. The purpose of this study was to explore the patterns of development of the immunity of the broiler chickens in cage.

Results: The results showed that there were 3 development patterns of immunity in the broiler chickens. The first pattern was Down-Up. Cytokines and some immune indicators first decreased and then increased, and the lowest levels of immunity basically occurred from d 6 to 13. The second pattern was Up-Down, and from d 30 to 34, the highest levels of non-specific cellular immunity components, such as the peripheral blood mononuclear macrophage ratio, specific cellular immunity components, such as the peripheral blood helper T (Th) cell ratio and T cell and B cell proliferation activity, and mucosal immunity components, such as the ileal CD4, TGF-β1 and IgA mRNA levels, were observed. The third pattern was Up-Up, and the levels of the non-specific cellular immunity components, such as the serum nitric oxide (NO), C3 and C4 levels, the specific cellular immunity components, such as the spleen index, peripheral blood IL-2, IFN-γ/IL-4, cytotoxic T (Tc) cell ratio, and splenic NF-κB mRNA levels, the humoral immunity components, such as the serum IgG level, the mucosal immunity components, such as the ileal MHC-II, CD3d, TCRβ subunit, TCRζ subunit, IFN-γ, pIgR mRNA and ileal mucosa sIgA levels, were continuing to increase from d 1 to 34.

Conclusions: It could be concluded that the immune system and its function have not developed well in the broiler chickens d 6 to 13 and that the immune system does not mature until d 30 to 34 in the broiler chickens in cages. It is necessary to enhance the immune function of the broiler chickens through nutritional measures from d 1 to 30.

Keywords: Age; Broiler chickens; Immunity development.

Fig. 1

The first immune development pattern in broiler chickens housed in laminated cages is Down-Up. The levels of IL-1β (a), IL-4 (b), IL-10 (c), IFN-γ (d) and IgA (e) in serum were analyzed by ELISA kit. The mRNA levels of IL-6 in spleen (f), IL-2 (g), IFN-γ/IL-4 (h) and Lysozyme C (i) in ileum were analyzed by RT-PCR. Different small letters indicated significant difference (P < 0.05)

Fig. 2

The second immune development pattern of broiler chickens housed in laminated cages is Up-Down. The frequencies of mononuclear/macrophage (a) and Th cells (b) of peripheral blood lymphocytes were analyzed by flow cytometry. Peripheral blood lymphocytes were stimulated with concanavalin A (ConA) (c) or lipopolysaccharide (LPS) (d), and the stimulation index (SI) was calculated as described in the Materials and Methods section. The mRNA levels of CD4 (e), IgA (f) and TGF-β1 (g) were analysed by RT-PCR. Different small letters on the bars indicated significant difference (P < 0.05)

Fig. 3

The third immune development pattern of broiler chickens housed in laminated cages is Up-Up. The levels of NO (a), C3 (b), C4 (c), IL-2 (d), IFN-γ/IL-4 (e), IgG (f) in serum and sIgA in ileum mucosa (p) were analyzed by ELISA kit. The frequencies of Tc cells (g) of peripheral blood lymphocytes were analyzed by flow cytometry. The spleen index was analyzed by weighing (h). The mRNA levels of NF-κB in spleen (i), MHC-II (j), CD3d (k), TCRβ subunit (l), TCRζ subunit (m), IFN-γ (n) and pIgR (o) in ileum were analyzed by RT-PCR. Different small letters indicated significant difference (P < 0.05)