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Evidence that TNF-induced respiratory burst of adherent PMN is mediated by integrin alpha(L)beta(2)
Eva Decleva1, Pietro Dri, Renzo Menegazzi
1Department of Physiology and Pathology, University of Trieste, Italy. declevae@univ.trieste.it
Abstract:
Polymorphonuclear leukocytes (PMN) respond to tumor necrosis factor (TNF) with a respiratory burst (RB) only after adherence to surfaces coated with extracellular matrix proteins such as fibronectin and fibrinogen (permissive substrates) but not with others such as laminin or collagen (nonpermissive substrates). As PMN adherence to both types of surfaces is dependent on beta(2) integrins, we investigated the molecular basis of the different metabolic response to TNF. In particular, we evaluated the relative role of each beta(2) integrin (alpha(L)beta(2), alpha(M)beta(2), and alpha(X)beta(2)) in adherence and O(2)(-) production of PMN residing on fibronectin- and laminin-coated surfaces, which were considered as models of permissive and nonpermissive surfaces, respectively. By using alpha chain-specific monoclonal antibodies (mAb), we show that alpha(M)beta(2) and alpha(X)beta(2) mediate adherence to fibronectin and laminin; alpha(L)beta(2) is not involved in adherence to laminin and has only a minimal contribution in adherence to fibronectin. Furthermore, production of O(2)(-) in response to TNF was induced by immobilized anti-alpha(L)beta(2) but not anti-alpha(M)beta(2) or anti-alpha(X)beta(2) mAb. A strong correlation was also found between expression of alpha(L)beta(2) and TNF-induced RB on fibronectin. Lastly, PMN responded to TNF on laminin with a RB after the inclusion of alpha(L)-specific mAb in the laminin coat. Thus, we conclude that TNF-induced RB by PMN residing on fibronectin is mediated by alpha(L)beta(2) and that alpha(M)beta(2) and alpha(X)beta(2) are likely to play an ancillary role to the signaling activity of alpha(L)beta(2) by facilitating its recruitment to sites of adherence. The nonpermissiveness of laminin appears to be a consequence of its inability to act as a ligand for alpha(L)beta(2).
Insights
Polymorphonuclear leukocytes (PMN) require specific surface proteins for activation by tumor necrosis factor (TNF). The alpha(L)beta(2) integrin is key for this response on fibronectin, while other integrins play supporting roles.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Polymorphonuclear leukocytes (PMN) are crucial immune cells involved in inflammatory responses.
- PMN activation by tumor necrosis factor (TNF) leading to a respiratory burst (RB) is dependent on their adherence to extracellular matrix proteins.
- Different extracellular matrix proteins act as permissive or nonpermissive substrates for PMN adherence and subsequent TNF-induced RB.
Purpose of the Study:
- To investigate the molecular mechanisms underlying differential PMN metabolic responses to TNF based on substrate adherence.
- To determine the specific roles of beta(2) integrins (alpha(L)beta(2), alpha(M)beta(2), alpha(X)beta(2)) in PMN adherence and RB induction on permissive (fibronectin) and nonpermissive (laminin) surfaces.
Main Methods:
- Utilized alpha chain-specific monoclonal antibodies (mAb) to block or activate specific beta(2) integrins.
- Assessed PMN adherence to fibronectin- and laminin-coated surfaces.
- Measured O(2)(-) production (RB) in response to TNF stimulation under various integrin-blocking or activating conditions.
Main Results:
- Alpha(M)beta(2) and alpha(X)beta(2) mediated PMN adherence to both fibronectin and laminin.
- Alpha(L)beta(2) played a minimal role in fibronectin adherence and was not involved in laminin adherence.
- TNF-induced RB was triggered by immobilized anti-alpha(L)beta(2) mAb, but not by anti-alpha(M)beta(2) or anti-alpha(X)beta(2) mAb.
- PMN responded to TNF on laminin with RB only when alpha(L)-specific mAb was included, indicating alpha(L)beta(2) engagement is necessary.
Conclusions:
- TNF-induced RB in PMN adhering to fibronectin is primarily mediated by the alpha(L)beta(2) integrin.
- Alpha(M)beta(2) and alpha(X)beta(2) likely support alpha(L)beta(2) signaling by facilitating its recruitment to adherence sites.
- The nonpermissiveness of laminin for TNF-induced RB is due to its inability to serve as a ligand for alpha(L)beta(2).