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The cell and molecular basis of leukocyte common antigen (CD45)-triggered, lymphocyte function-associated
H M Lorenz1, A S Lagoo, K J Hardy
1Birmingham Veterans Administration Hospital.
Insights
Cross-linking the leukocyte common antigen (CD45) on T cells triggers T-cell-monocyte aggregation via LFA-1/ICAM-1. This process uniquely involves cAMP/cGMP-dependent protein kinases, bypassing protein kinase C signaling.
Area of Science:
- Immunology
- Cellular Biology
- Molecular Signaling
Background:
- Leukocyte common antigen (CD45) cross-linking induces mononuclear cell aggregation.
- Lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) mediate these interactions.
Purpose of the Study:
- To investigate T-cell-monocyte interactions during CD45-induced aggregation.
- To elucidate the molecular signaling pathways involved in CD45-mediated aggregation.
Main Methods:
- Utilized purified T lymphocytes and monocytes.
- Compared signaling pathways of CD45 cross-linking versus phorbol myristate-12-13-acetate (PMA) stimulation.
- Assessed the effects of kinase inhibitors and cAMP-elevating agents.
Main Results:
- CD45-induced aggregation requires both T cells and monocytes.
- Cross-linking CD45 on T cells alone initiates aggregation.
- CD45-induced aggregation is independent of Fc-receptor signaling.
- CD45-induced aggregation is highly sensitive to H-8, a protein kinase inhibitor.
- PMA-induced aggregation, but not CD45-induced aggregation, is inhibited by PKC and tyrosine kinase inhibitors.
Conclusions:
- CD45 cross-linking on T cells induces LFA-1/ICAM-1-dependent T-cell-monocyte aggregation.
- This aggregation occurs via a novel signaling pathway.
- The pathway is independent of protein kinase C (PKC) and involves cAMP/cGMP-dependent protein kinases.
Abstract:
We recently reported that cross-linking the leukocyte common antigen (CD45) can rapidly induce aggregation of human peripheral blood mononuclear cells via lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) interactions. Herein, we have examined both T-cell--monocyte cellular interactions and the molecular signaling that are involved in this phenomenon. Experiments using highly purified T lymphocytes showed that CD45-induced aggregation requires the presence of both T cells and monocytes. Cross-linking CD45 only on T lymphocytes, but not on monocytes, initiated cellular clustering after reconstituting to the respective untreated cell type. By several criteria, CD45-induced clustering of T cells to autologous monocytes was shown to be Fc-receptor--independent. When comparing intracellular signaling in leukocyte aggregation induced by CD45 cross-linking versus phorbol myristate-12-13-acetate (PMA) treatment, the former was found to be fivefold to 10-fold more sensitive to H-8, a reagent that effectively blocks cAMP- and cGMP-dependent protein kinases. On the other hand, reagents that increase intracellular cAMP levels (eg, dbcAMP, forskolin, and IBMX), protein kinase C (PKC) inhibitors (eg, staurosporine), and tyrosine kinase inhibitors (eg, herbimycin A and genistein) all readily inhibited PMA-induced, but not CD45 monoclonal antibody-induced, aggregation. We conclude that cross-linking the leukocyte common antigen on T cells induces LFA-1--/ICAM-1--dependent T-cell--monocyte aggregation through a unique signaling pathway independent of PKC, which involves instead cAMP-/cGMP-dependent protein kinases.