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Engagement of ICAM-3 activates polymorphonuclear leukocytes: aggregation without degranulation or beta 2 integrin
M J Feldhaus1, J M Kessel, G A Zimmerman
1Department of Pathology, University of Utah, Salt Lake City 84112, USA.
Abstract:
ICAM-3 is a preferred counterreceptor for the leukocyte alpha(L)beta2 integrin. It activates T cells through outside-in signaling, but polymorphonuclear leukocytes (PMN) are reported to be refractory to ICAM-3 stimulation. We found that engagement of ICAM-3 by a mAb (CAL3.10), which binds in the region where alpha(L)beta2 integrin binds, activates PMN homotypic aggregation and adhesion to surfaces. These functional changes were due to ICAM-3 outside-in signaling because aggregation and adhesion were beta2 integrin-dependent, tyrosine kinase and protein kinase C activities were activated, and there was a reorganization of the cytoskeleton. This reorganization and kinase activity was required for ICAM-3-, but not FMLP-, induced aggregation. This is not an Fc-mediated event as an appropriate anti-ICAM-3 F(ab')2 fragment still induced aggregation. Another anti-ICAM-3 Ab (HP2/19), which activates T cells, did not activate PMN. Strikingly, anti-ICAM-3 did not induce degranulation or cause an increase in surface beta2 integrin expression, so adhesion and aggregation were due solely to the activation of the constitutively expressed beta2 integrins. Aggregation in response to ICAM-3, but not FMLP, was compromised at lower cell densities, showing that beta2 integrin recruitment enhances aggregation under suboptimal conditions. We conclude that engagement of ICAM-3 stimulates PMN as well as T cells, but that the appropriate epitope varies between these two cells. ICAM-3 outside-in signaling reorganizes the cytoskeleton without causing degranulation, induces serine and tyrosine kinase activation, and activates existing surface beta2 integrins to a proadhesive state.
Insights
Intercellular Adhesion Molecule 3 (ICAM-3) engages polymorphonuclear leukocytes (PMN), activating their aggregation and adhesion through outside-in signaling. This process involves cytoskeletal reorganization and kinase activation, distinct from T cell activation pathways.
Area of Science:
- Immunology
- Cell Biology
- Leukocyte Biology
Background:
- Intercellular Adhesion Molecule 3 (ICAM-3) is a key molecule in leukocyte interactions.
- While ICAM-3 activates T cells via outside-in signaling, polymorphonuclear leukocytes (PMN) were previously considered unresponsive.
- Understanding ICAM-3's role in PMN function is crucial for immune response insights.
Purpose of the Study:
- To investigate the functional response of PMN to ICAM-3 engagement.
- To elucidate the signaling pathways and molecular mechanisms underlying ICAM-3-mediated PMN activation.
- To determine if ICAM-3 can activate PMN despite their reported refractoriness.
Main Methods:
- Engagement of ICAM-3 on PMN using specific monoclonal antibodies (mAbs) and F(ab')2 fragments.
- Assessment of PMN homotypic aggregation and adhesion to surfaces.
- Analysis of intracellular signaling, including tyrosine kinase and protein kinase C (PKC) activity.
- Evaluation of cytoskeletal reorganization and surface molecule expression.
Main Results:
- ICAM-3 engagement by mAb CAL3.10 induced PMN homotypic aggregation and adhesion.
- These effects were dependent on beta2 integrin activation, tyrosine kinase, and PKC activity.
- ICAM-3 signaling led to cytoskeletal reorganization and activation of existing beta2 integrins, without degranulation.
- A distinct anti-ICAM-3 antibody (HP2/19) activated T cells but not PMN, suggesting epitope-specific responses.
Conclusions:
- ICAM-3 engagement activates PMN, contrary to previous reports, through a distinct outside-in signaling pathway.
- PMN activation by ICAM-3 involves cytoskeletal rearrangement and kinase activation, leading to enhanced adhesion and aggregation.
- The findings highlight differential epitope recognition of ICAM-3 between T cells and PMN, impacting immune cell function.