Adhesive interactions in thymic development: does selective expression of CD45 isoforms promote stage-specific...

CD45 isoform transitions appear to play essential roles in both life and death, and correlate with the stages of thymocyte development during which there is a change in physical location from medullary and/or outer cortical areas to the inner cortex. This work speculates that CD45 isoforms, through a focal role in the assembly of adhesive complexes mediated by the external domains, participate in the maintenance and/or modulation of migratory behaviour by differentiating thymocytes, or alternatively in the anchoring of thymocytes in a generative micro-environment. The objective of the sections that follow is to formulate the hypothesis that CD45 isoforms, through their differential interactions with adhesion molecules expressed by T cells, profoundly influence cell motility and consequent micro-environmental localization. An adhesive assembly of CD45 and adhesion molecules on the outside, and of the adhesive complex with the cytoskeleton on the inside, would promote CD45-mediated regulation of adhesion/de-adhesion through lateral external interactions mediated by external domains of CD45 isoforms, through enzymatic modulation of the cytoplasmic domains of adhesion molecules by the CD45 tyrosine phosphatase activity, and through phosphatase control of cytoskeletal assembly and disassembly.