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CD50 (intercellular adhesion molecule 3) stimulation induces calcium mobilization and tyrosine phosphorylation
M Juan1, O Viñas, M R Pino-Otín
1Servei d'Immunologia, Hospital Clínic, Barcelona, Spain.
Insights
Intercellular adhesion molecule 3 (ICAM-3), also known as CD50, plays a key role in T cell activation. Cross-linking CD50 on Jurkat cells triggers calcium influx via protein-tyrosine kinases, suggesting its involvement in immune responses.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- CD50, identified as ICAM-3, is a counter-receptor for LFA-1.
- CD50 is implicated in initial immune response adhesion events.
Purpose of the Study:
- To investigate the molecular events following CD50 cross-linking on T cells.
- To elucidate the role of CD50 in leukocyte interactions and T cell activation.
Main Methods:
- Incubation of Jurkat cells with anti-CD50 mAbs and cross-linking antibodies.
- Measurement of intracellular calcium concentration ([Ca2+]i).
- Tyrosine phosphorylation analysis, including immunoprecipitation and in vitro kinase assays.
Main Results:
- CD50 cross-linking induced a significant rise in [Ca2+]i, primarily from extracellular calcium uptake.
- This calcium flux was dependent on tyrosine phosphorylations and enhanced by CD3 costimulation.
- Protein-tyrosine kinases, specifically p56lck and p59fyn, were found in CD50 immunoprecipitates.
Conclusions:
- CD50 signaling involves protein-tyrosine kinases (PTK).
- CD50 interaction with LFA-1 may lead to T lymphocyte activation.
- CD50 plays an active role in T cell activation following antigen triggering.
Abstract:
The leukocyte differentiation antigen, CD50, has been recently identified as the intercellular adhesion molecule 3 (ICAM-3), the third counter-receptor of leukocyte function-associated antigen 1 (LFA-1). This molecule seems to be specially involved in the adhesion events of the initial phases of the immune response. To characterize the role of CD50 in leukocyte interactions, the different molecular events induced after cross-linking of CD50 on T cell-derived Jurkat cell line have been analyzed. When cells were incubated with anti-CD50 mAbs and cross-linked with polyclonal goat anti-mouse immunoglobulins, a rise in intracellular calcium concentration ([Ca2+]i) was observed. This increase in [Ca2+]i was mainly due to the uptake of extracellular Ca2+. This Ca2+ flux involved tyrosine phosphorylations and was further increased by CD3 costimulation. These data, together with those obtained by phosphotyrosine (P-Tyr) immunoprecipitation and in vitro kinase assays, suggested the involvement of protein-tyrosine kinases (PTK) in CD50 transduction pathways. By using specific antisera, the presence of p56lck and p59fyn protein tyrosine kinases (PTK) was clearly demonstrated in the CD50 immunoprecipitates. These findings suggest that the interaction of CD50 with its natural ligand (LFA-1) may result in T lymphocyte activation events, in which CD50 could play a very active role after antigen triggering.