Effect of heat stress on cellular and humoral immunity and its cure with α-tocopherol in meat type birds

Abstract

The aim of this study was to judge against the association of high dietary levels of α-tocopherol supplementation during heat stress on the immune response of meat type birds. Peritoneal macrophages (MΦ) were isolated and their in vitro cytotoxic activity was assessed against opsonized sheep red blood cells (SRBC) along with their nitric oxide (NO) production, blood heterophil to the lymphocyte ratio (H:L), mitogenic response to phytohemagglutinin-P (PHA-P), antibody production to SRBC together with IgM and IgG titers and serum cortisol concentration. Two groups of broilers were maintained at 41±3°C without and with supplementation of α-tocopherol (3g/Kg feed) and sampling was carried out on 21st, 28th, 35th and 42nd days of age. The supplementation of α-tocopherol significantly (P≤0.05) enhanced the capacity of MΦ to engulf unopsonized SRBC after 14 and 21 days of treatment. However, the MΦ engulfment of opsonized SRBC and engulfment/cell remained significantly more (P≤0.05) during the whole experiment. Macrophage NO production was increased in all the treatments with the increase in age of birds while the NO production was maximum with lipopolysaccharides (LPS) stimulation, when birds were under supplementation of α-tocopherol. The H:L and PHA induced toe web thickness both were significantly higher (P≤0.05) in α-tocopherol fed group as compared to control. We found a dose-dependent boost in antibody titer production in response to SRBC at 35th and 42ndd of age of α-tocopherol supplemented group. Serum IgG titer remained same after the 28thd of age irrespective of the treatment while there was a significant increase (P≤0.05) in the serum IgM titer. Serum cortisol concentration was significantly lower (P≤0.05) in α-tocopherol supplemented group rather than control. Our study validates the use of increased α-tocopherol level supplementation to achieve better immunomodulation during stress conditions.