Age-related structural modulation of T lymphocyte-associated CD45 isoforms.
A monoclonal antibody, specific to all conventional CD45 isoforms, was employed in two-dimensional (2D) sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting to investigate possible age-related differential expression of these isoforms among immature and mature thymocytes as well as CD4+ and CD8+ T cell subpopulations in the periphery of newly-born, young and aged BALB/c mice. In young mice, and to a lesser degree in newly-born mice, intra-thymic maturation seemed to be paralleled by the capacity of thymocytes to synthesize distinct CD45 isoforms constituted by extensively heterogeneous acidic charge entities. Thymocyte maturation in aged mice, on the other hand, was characterized by minimal heterogeneity, as the observed pattern was essentially similar to the immature population in 2D blots. As inferred from comparisons of 2D blots of sialylated and desialylated forms of the CD45 complex, age-related differences in isoforms expressed by the CD4+ and the CD8+ T cell subpopulations in the periphery resided mainly in the degree of sialylation of the constituent isoforms. Given the potential of the differential sialylation state of CD45 in altering the recognition properties of lymphocytes, regulation of CD45 sialylation with age may add another level of complexity to the lymphocyte surface phenotype, which in turn may be implicated in cell-cell interaction mechanisms during lymphocyte maturation and senescence.