Antigen exposure occurs throughout an individual's life and can be due to various factors:
Infections: Exposure to various pathogens, including bacteria, viruses, fungi, and parasites, can stimulate an immune response and lead to the generation of memory T cells. Repeated exposure to the same pathogen or cross-reactive antigens can contribute to the accumulation of antigen-specific T cells, some of which may become senescent over time.
Latent viral infections: Certain viruses, such as cytomegalovirus (CMV), Epstein-Barr virus (EBV), and varicella-zoster virus (VZV), can establish lifelong latent infections. These persistent infections can continuously stimulate T cells, leading to the accumulation of virus-specific T cells, many of which display a senescent phenotype.
Vaccinations: Vaccines expose the immune system to specific antigens to generate a protective immune response. While vaccines are essential for preventing infectious diseases, they also contribute to the accumulation of antigen-specific memory T cells over an individual's lifetime.
Environmental antigens: Exposure to environmental antigens, such as pollens, dust mites, and pet dander, can trigger immune responses in some individuals and lead to the generation of antigen-specific T cells.
Food antigens: In some cases, exposure to certain food proteins can stimulate an immune response, particularly in individuals with food allergies or sensitivities.
Self-antigens: In autoimmune disorders, the immune system mistakenly recognizes self-antigens as foreign and mounts an immune response against the body's own tissues. This can lead to the accumulation of self-reactive T cells, some of which may become senescent.
Chronic inflammation: Persistent low-grade inflammation, which can be caused by factors such as obesity, stress, and age-related processes, can expose T cells to inflammatory mediators and contribute to their differentiation and senescence.
The accumulation of senescent T cells is a gradual process that occurs over an individual's lifetime due to the combined effects of these various sources of antigen exposure.
