CD45; from alloantigen to mapping of restricted epitopes using recombinant soluble CD45 isoforms.

The two main themes of this symposium centre on the roles played by the intracellular and extracellular parts of the CD45 antigen. The intracellular part has been characterized as a protein tyrosine phosphate phosphatase with an important role in lymphocyte activation. The extracellular part shows antigenic heterogeneity that has been of value in the recognition of subpopulations of lymphocytes, and in particular in dividing CD4-positive T lymphocytes into functional subsets. Interestingly two of the other markers that have been used to subdivide this population were, like CD45, originally defined with alloantisera namely the Thy-1 [ 11 and RT-6 [peripheral thymus-derived antigen (Pta)] antigens [Z].