Differential expression of inducible nitric oxide synthase is associated with differential Toll-like receptor-4 expression in chicken macrophages from different genetic backgrounds

The purpose of this study was to examine iNOS gene expression and activity in macrophages from different chicken genetic lines against various bacterial LPS. Furthermore, the possible involvement of surface LPS receptors as candidates for differential iNOS gene induction in these genetic lines of chicken was also examined. Sephadex-elicited abdominal macrophages (1 x 10(6)) as well as iNOS hyper-responder macrophages from a transformed chicken macrophage cell line, MQ-NCSU, were exposed to 5 mug/ml LPS from E. coli, Shigella flexneri, Serratia marcensces, and Salmonella typhimurium. Nitrite levels were quantitated in the culture supernatant fractions of macrophages after 24 h by the Griess method. The results showed that macrophages from K-strain ((BB15)-B-15) (range from two separate trials: 31-89 muM) and MQ-NCSU (22-81 muM) were high responders whereas macrophages from both GB1 ((BB13)-B-13) (15-38 muM) and GB2 ((BB6)-B-6) (7-15 muM) chickens were low responders against all LPSs used. Northern blot analysis revealed that K-strain macrophages expressed higher intensity of 4.5 Kb iNOS mRNA (iNOS/beta-actin ratio) than macrophages from GB2 regardless of the LPS source. To elucidate possible molecular mechanism(s) involved in iNOS gene expression in these two strains of chickens, the constitutive expression of LPS-related macrophage cell surface receptors, CD14, Toll-like receptor-2 (TLR2), and Toll-like receptor-4 (TLR4), was examined via flow cytometry using anti-human CD14, TLR2 and TLR4 antibodies. CD14 surface expression and intensity was not different between macrophages from K-strain or GB2 chickens. In contrast, while the overall percentage of TLR4-positive macrophages was the same (K-strain, trial 1 = 92%, trial 2 = 62%; GB2, trial 1 = 91%, trial 2 = 64%), the mean fluorescence intensity (MFI), an indicator of receptor number, was significantly higher (P = 0.05) in K-strain macrophages (MFI: trial 1 = 145; trial 2 = 131) than GB2 macrophages (MFI: trial 1 = 101; trial 2 = 98). Furthermore, TLR2 (a previously thought candidate as LPS signaling molecule) positive cell numbers were higher in K-strain than the GB2 macrophages in one of the two trials with no difference in the intensity of TLR2 expression in either trial. These findings suggest that the observed differences in iNOS expression and activity among the K-strain (hyper-responder) and GB2 (hypo-responder) chickens are, at least in part, due to differential expression of TLR4 (an LPS signaling molecule), leading to more intense LPS-mediated activation of K-macrophages. (C) 2002 Elsevier Science B.V. All rights reserved.