Immune reactivity during ageing III. Removal of peanut-agglutinin binding cells from ageing mouse spleen cells leads to increased reactivity to mitogens

Spleen cells from ageing (24-30-month-old) mice, manifesting low response to concanavalin A (Con A) and phytohemagglutinin (PHA), were separated by peanut agglutinin (PNA) into agglutinable (PNA⁺) and unagglutinable (PNA^-) fractions. The PNA⁺ cells were found to suppress the response of young (2-3-month-old) mouse spleen cells to the mitogens Con A and PHA. On the other hand, PNA^- cells of the ageing mice expressed a response to these mitogens, at levels higher than those of the unseparated cells. Re-mixing of the PNA^- and PNA⁺ cells of the ageing mouse spleens at various proportions indicated that the PNA^- cells are indeed suppressible by the PNA⁺ cells. Anti Thy-1.2 treatment to the PNA⁺ fraction suggested that this suppression was not exerted by T cells. It thus appears that at least part of the reduced lymphoid cell function in ageing is related to an effect of suppressor cells, interfering with the expression of available reactive cells.