Humoral immunity in aging.

The interactions between B and T lymphocytes, leading to the development of humoral responses, are reviewed with references to the changes occurring in aged people. Aging is perceived as a process of impairment of immune functions; it is known that T cells from aged subjects have a reduced ability to produce IL-2. However, other functions seem to be upregulated in elderly subjects; indeed, IL-1, IL-3, IL-4, IL-6 and TNF alpha production are increased both in aged mice and humans. These cytokines are known to control B cell differentiation, through isotype switch and Ig production. A significant increase in IgG subclasses and IgA is observed in sera of aged subjects. This contrasts with the significant decrease in circulating B lymphocytes. The impairment of primary responses to immunization, and other aspects of humoral immunity, including mucosal responses, autoantibody production and correlations with phenotypic markers of T and B cell subsets, are discussed.