Cluster Formation by Protein Kinase Cθ during Murine T Cell Activation: Effect of Age

Protein kinase Cθ (PKCθ) is thought to play an important role in T cell activation, in that exposure of cloned T cells to antigen-presenting cells bearing agonist peptides, but not antagonist peptides, leads to clustering of PKCθ molecules in the section of the T cell plasma membrane that is in contact with the APCs. To see whether aging affects this PKCθ clustering reaction in mouse T lymphocytes, we used immunofluorescence staining and confocal microscopy to observe the localization of PKCθ in CD4 and CD8 T lymphocytes activated by coincubation with anti-CD3 hybridoma cells. Aging led to a twofold decline in the proportion of both CD4 and CD8 T cells in which PKCθ underwent cluster formation. This decrease with age was not due to differences in the number of cell conjugates formed, nor to kinetic differences of PKCθ clustering, nor to the accumulation of memory T cells in old mice. There were no effects of aging on the levels or kinase activity of PKCθ in murine T cells. Our data suggest alterations in the upstream signals that regulate PKCθ translocation.