Immunosenescence refers to the gradual deterioration of the immune system brought on by natural age advancement. It involves both the host’s capacity to respond to infections and the development of long-term immune memory, especially by vaccination. This age-associated immune deficiency is ubiquitous and found in both long- and short-living species as a function of their age relative to life expectancy rather than chronological time. It is considered a major contributory factor to the increased frequency of morbidity and mortality among the elderly.

Immunosenescence is not a random deteriorative phenomenon, rather it appears to inversely repeat an evolutionary pattern and most of the parameters affected by immunosenescence appear to be under genetic control. Immunosenescence can also be sometimes envisaged as the result of the continuous challenge of the unavoidable exposure to a variety of antigens such as viruses and bacteria.

Immunosenescence is a multifactorial condition leading to many pathologically significant health problems in the aged population. Some of the age-dependent biological changes that contribute to the onset of immunosenescence are listed below: