Cluster formation by protein kinase Ctheta during murine T cell activation: effect of age

Protein kinase Ctheta; (PKCtheta;) 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 PKCtheta; molecules in the section of the T cell plasma membrane that is in contact with the APCs. To see whether aging affects this PKCtheta; clustering reaction in mouse T lymphocytes, we used immunofluorescence staining and confocal microscopy to observe the localization of PKCtheta; 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 PKCtheta; underwent cluster formation. This decrease with age was not due to differences in the number of cell conjugates formed, nor to kinetic differences of PKCtheta; 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 PKCtheta; in murine T cells. Our data suggest alterations in the upstream signals that regulate PKCtheta; translocation.