The CD45 tyrosine phosphatase: a positive and negative regulator of immunecell function

The CD45 phosphotyrosine phosphatase is one of the most abundant glycoprote ins expressed on immune cells. Previously, the serpentine twists and turns of the CD45 research field have tended to draw attention to CD45 either as a positive or negative regulator of immune cell function. This review draws heavily on CD45 knockout mouse data to emphasize that CD45 has both positi ve and negative actions in regulating receptor thresholds, and these roles vary according to cell lineage and developmental stage. Previously conflict ing results are reconciled in a model suggesting how CD45 regulates the p58 (lck) tyrosine Kinase in T cell signalling and development.