Age-related changes in responsiveness of various rat tissue lymphocytes to mitogens

The effect of age on the mitogen responses of rat lymphoid tissues was investigated. Evaluation was based on using the in vitro proliferative response of lymphocytes from various tissues of Fischer-344 rats (2, 7, 13, 19 and 25 months) using concanavalin A (Con A), phytohemagglutinin-P (PHA-P), pokeweed mitogen (PWM) and Mycoplasma neurolyticum. The stimulation index (S. I.) for cervical, mesenteric, thymic and splenic lymphocytes treated with Con A and PHA-P was greatest for 2-month-old rats and lowest for 19-month-old rats; however, no age-related change was observed with either PWM or M. neurolyticum. The levels of mitogenic responses for lymph nodes in the two different anatomical sites paralleled one another, with the cervical lymphocytes showing a greater response. The splenic lymphocytes responded less than either lymph node lymphocyte population. When PHA-P treatment of splenic lymphocytes followed the removal of the plastic adherent population, the S. I. of the resulting non-adherent population was comparable to the S.I. of other tissue lymphocytes; however, an age-related decrease was still observed. The PHA-P proliferative response of either the 7- or 19-month non-adherent population was suppressed by the 7-month adherent population and not by the 19-month adherent population, i.e., adherent population interaction with non-adherent population decreases with age.