Abstract
Several different approaches have been used for assessment of the mechanisms of B cell activation. In normal subjects, the circulating B cell pool contains B cells at various stages of activation. The resting B cells can be induced by T cell-independent B cell mitogen, Staphylococcus aureus Cowan I (SAC) to undergo proliferation. The partially activated B cells, when provided with adequate T cell help, can proliferate and differentiate into immunoglobulin (Ig)-secreting cells under the influence of either SAC or pokeweed mitogen (PWM). The fully differentiated B cells are represented by the numbers of cells in the peripheral blood that secrete Ig spontaneously.
We evaluated B lymphocyte function in 24 elderly (mean 79.3 yr.) and 14 young (mean 24.5 yr.) persons. Lymphocytes from elderly persons incorporated significantly less tritiated thymidine as compared with lymphocytes from young persons when stimulated with SAC. Moreover, the elderly, but not young, persons were found to have elevated numbers of cells spontaneously secreting Ig. However, lymphocytes from elderly persons stimulated with either SAC or PWM displayed Ig production equal to young persons. These results in elderly persons are consistent with polyclonal B cell activation in vivo, as can be seen after certain viral infections and in some autoimmune diseases. The potential role of age-related B cell abnormalities in the increase with age in the incidence of infections, neoplasia, immune deficiency, and diseases that may be mediated by immune complexes is discussed.
