LPS Ligation of TLR4 on Alveolar Macrophages Promotes PMN and CDR+ T Cell Transendothelial Migration

Abstract

A hallmark feature of ALI/ARDS is pulmonary leukocyte infiltration. Previous studies indicate that both PMN and CD3 T cells infiltrated the lungs of mice after challenge with LPS (i.t.). Herein, we assessed the role of alveolar macrophages (AM) in the leukocyte emigration in vivo and in vitro. AM were depleted by intra-tracheal administration of liposomes containing dichloromethylene diphosphonate (C2MDP); liposomes containing PBS served as controls. The LPS-induced infiltration of alveoli by PMN and CD3 T cells was substantially blunted in AM-depleted mice (immunohistochemistry). These observations indicate that LPS-activated AM play an important role in promoting both PMN and T cell emigration from the vasculature into the alveoli. Using a transwell system we assessed the role of AMФ (BAL fluid) TLR4 on PMN (bone marrow derived) and CD4⁺ T cells (enriched from splenocytes) migration across endothelial cell monolayers (derived from lungs). Challenge of AMФ with LPS induced transendothelial migration of both PMN and CD4⁺ T cells. When AMФ isolated from TLR4-/- mice were used in the assay, the transendothelial migration of both PMN and CD4⁺ T cell was substantially blunted. Grant Funding Source: KACST – MED 1672-44