The immune system is highly sensitive to shortening of telomeres since its effectiveness depends on immune cells, specifically white blood cells, ability to proliferate during times of immunological stress.

Although cells of the immune system are unique in that they can up-regulate telomerase unlike other somatic cells, when telomeres of lymphocytes reach a critical minimum length, the ability to activate telomerase in lymphocytes is diminished and adaptive immunity becomes compromised.

Less effective immune response means more infections, increases oxidative stress, inflammation and less defenses against cellular stresses

Individuals with shorter white blood cell telomeres have an 8-fold higher mortality rate for infectious diseases.

The expansion of lymphocytes when confronted with an antigen results in major cell proliferation. Each immune response typically results in 15-20 cell divisions. Once these cells eliminate the antigen, they will usually undergo apoptosis although a few will remain which gives a person life-long immunity to various pathogens. Research has shown that the telomeres of these lymphocytes which have undergone major cell division, but still remain as memory cells do, in fact, have shorter telomeres. Since the immune system depends on the ability of lymphocytes to undergo cell division in response to antigens, telomere shortening can severely limit a person’s immunological defenses.