Submitted to: Avian Immunology Research Group Abstract
Publication Type: Abstract only
Publication Acceptance Date: 4/4/2011
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Macrophages play significant role in immunity which not only kill pathogens, produce cytokines but also clear dead tissues at the site of inflammation and stimulate wound healing. Much less is known how these cells contribute to tissue repair process. In course of our studies comparing the peptide profiles of chicken monocytes and heterophils, we found monocytes rich in thymosin beta 4 (Tb4), a peptide with multiple biological functions such as angiogenesis and wound healing. Intracellularly Tb4 binds to cytoskeletal actin to regulate cell motility and phagocytosis. We hypothesized that Tb4 production may be dynamically regulated by the factors which activate macrophage and facilitate their tissue repair function. Using toll-like receptor (TLR) activating ligands we evaluated their effects on Tb4 production by a transformed chicken macrophage cell line HTC at 6 and 24h after stimulation. Stable isotope labelling of amino acids in cell culture (SILAC) and mass spectrometry was used to monitor the changes in cellular and conditioned media (CM) Tb4. Real time PCR and metabolite measurements were used to determine macrophage activation. None of the TLR agonists showed any significant change in either cellular or CM Tb4 levels at 6h but some agonists such as LPS, peptidoglycan (PGN), and CpG induced the expression of interleukins-1beta, -6, and nitric oxide synthase genes but not Tb4 at that time point. Nitrite accumulation was discernible at both time points supporting gene expression results. At 24 h time point however, the same agonists caused significant depletion of cellular Tb4 with its concomitant detection in the CM. The CM also contained Tb4 sulfoxide, a metabolite with anti inflammatory efficacy. Incongruity between the Tb4 gene expressions along with its release into the CM at 24 h without the possibility of its replenishment, suggested that only macrophage death could cause its externalization. To verify we determined the percentage of trypan blue positive cells and lactate dehydrogenase (LDH) activity of the CM as indicators of cell death. The results showed that the TLR agonists which induced depletion of intracellular Tb4 also increased macrophage death implying that these highly dynamic cells may contribute to wound healing process by their ultimate sacrifice.