T lymphocytes, as a component of the immune system, play a vital role in defending our body against intracellular pathogens, such as viruses, intracellular bacteria or parasites. In a previous blog we mentioned that cellular functions can abate with aging and cause the marked reduction in immune system responsiveness. These changes have been associated with increased morbidity and mortality in the elderly population from infectious diseases.
Aging affects the functions of T lymphocytes in a myriad of ways. One of the major changes that occur is the reduction in naive T cells population caused by thymic involution. As these cell age, they also lose their capacity to maintain the homeostatic proliferation that balance and maintain their pool.
A naive T cell becomes activated and stimulated on encounter to any foreign antigens. In this process some of the naive T cells will convert into memory T cells that protect us from subsequent exposure to the same pathogen.
A robust T lymphocyte response is required to protect the host against a variety of pathogens. In aging adults, the number of precursor naive T cell decreases drastically. In addition to a reduction in naïve T cell population, old pathogenic memory (VM) precursor cells also exhibit selective impairment in response to T cell receptor (TCR) signals relative to naïve T cell counterparts. These two separate defects combine and contribute to reduced cell response in regards of aging. This finding will provide an understanding of potential immune intervention in older adults. Furthermore, TCR signals play a very critical role not only in the maintenance of naive T cells but also for the emergence of pathogenic memory CD8+ cells. These CD8+ T cells with T cell receptors recognize and attack pathogen-infected cells.
In a nutshell, T cell aging is allied to compromised cell receptor signals received by naïve T cells, which in turn not only impaired the conversion to become virtual memory cells but also gradually ‘burn’ their ability to divide in response to infection. The above finding could provide a key to understand the immune response as we age.
 Murasko, D. M., and J. Jiang. 2005. Response of aged mice to primary virus infections. Immunol. Rev. 205: 285–296.
 Naylor, K., G. Li, A. N. Vallejo, W. W. Lee, K. Koetz, E. Bryl, J. Witkowski, J. Fulbright, C. M. Weyand, and J. J. Goronzy. 2005. The influence of age on T cell generation and TCR diversity. J. Immunol. 174: 7446–7452