What is the primary effect of aging on the immune system?

Aging primarily impacts the immune system by decreasing the function of T cells. As individuals age, the thymus, which is responsible for the maturation of T cells, undergoes atrophy, leading to a reduction in the output of new T cells. This decline in T cell quantity and functionality affects the body's ability to respond effectively to new infections and reduces the overall adaptability of the immune response.

The diminished function of T cells also leads to impaired cellular immunity, making it more difficult for the elderly to combat viral infections and to mount appropriate responses to vaccines. This can result in increased susceptibility to infections and less effective vaccine responses, highlighting the critical role that T cells play in maintaining immune competence.

Although aging is associated with a decrease in B cell production and other aspects of the immune system, the most significant and notable impact is observed within the T cell compartment. This decline in T cell function is a key factor that significantly affects the overall immune landscape in older adults.