Analysis of immature B cell activation and differentiation

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To study the activation and development of immature B lineage cells, we searched the unique signal transduction molecules expressed in the immature B cells or in the process of B cell activation.We characterized the pre-BCR signal transduction molecules, among which PI-3 kinase activity was shown to be involved in the pre-B cell stages. We also isolated a molecule named immunoglobulin-receptor binding protein (IGBP-1/alpha4) , which is originally identified as a phosphoprotein co-precipitated with the BCR-component MB-1 molecule. The alpha4 gene was isolated and characterized. The recent results also showed that the alpha4 protein is associated with the protein phosphatase 2 A,whose association is critical for the proliferation of B cells. The alpha4/PP2A complex is shown to be a novel target of rapamycin. These results implicated the novel signal transduction pathway involved in the proliferation of lymphoid cells.