Altered Composition of the Immunological Synapse in an Anergic, Age-Dependent Memory T Cell Subset1

In young mice, memory CD4 T lymphocytes with high P-glycoprotein activity (P-gphigh) are unresponsive to TCR stimulation in vitro but can be activated by PMA plus ionomycin. The proportion of these hyporesponsive cells increases considerably with age. The earliest events in T cell activation were studied in P-gphigh and P-gplow CD4 memory cells at the single-cell level using confocal immunofluorescence methods. Recruitment of both linker for activation of T cells (LAT) and protein kinase C-θ to the immunological synapse, i.e., the site of T cell interaction with stimulator cells, was greatly impaired in P-gphigh cells from both young and old mice. Translocation of NF-AT to the nucleus, CD69 expression, and proliferative capacity were also diminished to a similar extent in P-gphigh cells under the same activation conditions. In contrast, movement of c-Cbl to the synapse region occurred in a high proportion of CD4 memory T cells regardless of P-gp subset or age. Moreover, although P-gplow cells frequently recruited both c-Cbl and LAT to the APC synapse, cells in the less responsive P-gphigh subset frequently relocated c-Cbl, but not LAT, to the interface region. In some systems, c-Cbl can act as a negative regulator of receptor-dependent tyrosine kinases, and alterations of c-Cbl to LAT ratios in the P-gphigh subset may thus contribute to the hyporesponsiveness of this age-dependent, anergic memory cell population.