Expression of toll like receptors (TLR3 and TLR4) during growth and sexual maturity of indigenous chicken ‘Sikhar’ of Mizoram

Sikhar bird is desi/local type of chicken found in Mizoram which can thrive and produce with irregular supply of feed and water and with minimum healthcare (Padhi 2016, Mayengbam et al. 2017). This chicken is of scavenging type and is being reared purposely for catching Red Jungle Fowl from the forest areas (Mayengbam et al. 2017). Genetically distant chicken lines were found to show different patterns of TLR genes expression with higher expression of toll like receptore (TLR) 3 mRNA in White Leghorns and of TLR4 and TLR5 mRNA in indigenous chicken like Aseel and Kadaknath (Ramasamy et al. 2010). Higher expression of TLR4 in heterophils had been indicated to be a marker for higher level of innate immunity in indigenous chicken (Ramasamy et al. 2011) and expression of Nicobari chicken TLR2, TLR3, TLR4, TLR5, TLR15 and TLR21 were found to be influenced by immunomodulatory phytochemicals (Sunder et al. 2016). Being an indigenous chicken, Sikhar birds are also expected to possess different expression profiles for different TLRs. The study was carried out in Sikhar bird of Mizoram reared in the backward rearing system where the climate was tropical monsoon type. Blood was collected from jugular vein of five different groups, viz. group 1 (2 months old), group 2 (4 months old), group 3 (6 months old), group 4 (8 months old) and group 5 (10 months old). Each group comprised 12 birds of either sexes. The body weight recorded were 217.92±7.11, 484.67±21.69, 728.33±27.38, 1010.80±67.21 and 1134.20±69.58 g in groups 1, 2, 3, 4 and 5 respectively as reported earlier (Mayengbam et al. 2017). Time to time behavioural changes of each of the birds was recorded in respect of their age and sex. Plasma concentration of TLR3, TLR4, thyroid stimulating hormone (TSH), tri-iodothyronine (T3), thyroxine (T4) and follicle stimulating hormone (FSH) were estimated by using commercially available enzyme link immunosorbent assay (ELISA) kits from Cusabio Biotech Co. Ltd., China for TLR3, TLR4, TSH, T3 and T4 and YH Biosearch Laboratory, China for FSH. Data were subjected to one way ANOVA for statistical significance followed by Duncan’s post hoc multiple comparisons to evaluate the differences between different age groups on all the parameters under the study and P<0.05 was accepted as statistically significant. Plasma concentration of TLR3, TLR4, TSH, T3, T4 and FSH of Sikhar birds in different age groups is presented in Table 1. During young age at 2 months, the plasma concentration of TLR3 could not be estimated with ELISA which could be due to too low concentration of plasma TLR3 which was below the detectable range of the ELISA kit used. There was increase in TLR3 expression with age (Table 1). TLR3 was stable till the age of 8 months and increased significantly (P<0.05) at 10 months of age (Table 1). Previous studies also revealed lower expression of TLR3 mRNA in heterophils of indigenous chicken as compared to White Leghorn chicken (Ramasamy et al. 2010). Due to