Related Experiment Videos
Lymphocyte chemoattractant factor induces CD4-dependent intracytoplasmic signaling in lymphocytes
W W Cruikshank1, J L Greenstein, A C Theodore
1Pulmonary Center, Boston University School of Medicine, MA 02118.
Insights
Lymphocyte chemoattractant factor (LCF) directly interacts with CD4 receptors on lymphocytes. This interaction triggers intracellular calcium and inositol trisphosphate signaling, crucial for immune cell communication.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- The soluble ligand for CD4, a critical receptor on T helper cells, remains poorly characterized.
- While MHC class II molecules are known to bind CD4, in vivo demonstration of this interaction is challenging.
Purpose of the Study:
- To investigate if lymphocyte chemoattractant factor (LCF) directly binds to CD4.
- To determine if LCF binding to CD4 induces intracellular signaling pathways.
Main Methods:
- CD4 affinity purification was used to isolate natural and recombinant LCF.
- Intracellular calcium levels and inositol trisphosphate generation were measured in CD4+ lymphocytes and transfected cell lines.
- The effect of LCF was assessed in the presence of anti-CD4 antibodies.
Main Results:
- LCF induced a significant rise in intracellular calcium and inositol trisphosphate in CD4+ cells.
- Cell lines lacking CD4 or expressing a truncated CD4 molecule did not show these signaling responses.
- Anti-CD4 antibodies blocked the LCF-mediated signaling.
Conclusions:
- LCF directly interacts with the CD4 molecule.
- This interaction initiates downstream second messenger generation, suggesting a novel signaling pathway for LCF via CD4.
Abstract:
At present, a naturally occurring soluble ligand for CD4 has not been well described. There is much evidence to indicate that MHC class II molecules can bind to CD4; however, binding of intact class II molecules under physiologic conditions has been difficult to demonstrate. We investigated whether a previously reported human lymphokine, lymphocyte chemoattractant factor (LCF), which was described for its effects on human CD4+ lymphocytes and monocytes, could associate directly with CD4 and induce the generation of second messengers. In the present study, we demonstrate that CD4 affinity-purified natural and recombinant LCF induced a rise in intracellular calcium and increased inositol trisphosphate generation in normal human CD4+ lymphocytes and murine T cell hybridomas infected to express human CD4. Cell lines lacking human CD4 or expressing human CD4 molecules that lack the intracytoplasmic domain did not demonstrate a change in either calcium or inositol trisphosphate. The effect of LCF was blocked by coincubation with either anti-CD4 antibody or Fab fragments from anti-CD4 antibody. These studies demonstrate direct interaction of a lymphokine with CD4 and generation of second messengers as a result of the interaction.