Role of Regulatory T Cells on the Age-Related Increase in Mitogen-Induced IgG Production in Vitro by Human Lymphocytes

When in vitro IgG production by mitogen-stimulated peripheral lymphocytes from healthy aged (70-93 year old) and young (20-29 year old) subjects was compared, it was found that the level of IgG production was elevated in the aged subjects. Co-culture studies were performed to determine whether the increase was clue to changes in T or non-T cells. IgG production was significantly higher when reference non-T cells from normal young adults were mixed with T cells from aged subjects than with T cells from young adults. In contrast, no significant difference in IgG production was observed when reference T cells from normal young adults were mixed with non-T cells from either young or aged subjects. The suppressor activity of Tγ cells and helper activity of non-Tγ T cells of young and aged subjects were then determined. The results revealed that the suppressor activity of Tγ cells of aged individuals was significantly lower than that of young adults, but the helper activity of non-Tγ T cells of young and aged subjects was comparable. These results indicate that the increase in production of IgG by the peripheral lymphocytes of aged individuals is due in part to changes in the T cells which are related to a decrease in suppressor activity of Tγ cells.