Antigen-specific CD4 T cell clonal expansion and differentiation in the aged lymphoid microenvironment. I. The primary T cell response is unaffected

Aging is associated with changes in the immune system that lead to decreased immunity in the elderly. Prior studies from humans and mice have shown that aged T cells exhibit numerous defects, including decreased proliferation following in vitro stimulation, suggesting that intrinsic defects exist within aged T cells, leading to defective T cell activation and clonal expansion. In vivo, however, cellular and soluble factors in the lymphoid microenvironment influence T cell function. To investigate the effects of the aged lymphoid microenvironment on T cell function, we monitored the immune response of CD4 T cells from DO11.10 TCR transgenic mice following adoptive transfer into young and aged hosts. After immunization with specific antigen similar rates of donor DO11.10 T cell division were observed in the two host types. However, at the peak of the response, greater numbers of DO11.10 T cells were found in the aged hosts. Regardless of the age of the host, the donor DO11.10 T cell population differentiated into functional effector cells. Despite the increased CD4 T cell growth in aged hosts, similar numbers of memory DO11.10 T cells were found in young and in aged hosts. As CD4 T cell clonal expansion and differentiation is not impaired in the aged microenvironment, our data suggest that diminished T cell immunity during aging is largely due to intrinsic T cell defects, rather than to extrinsic influences associated with the aged lymphoid microenvironment.