Age-related Refractoriness of PHA-induced Lymphocyte Transformation. I. Comparable Sensitivity of Spleen Cells from Young and Old Mice to Culture Conditions

The decline in phytohemagglutinin (PHA) responsiveness of spleen cells from aged mice was studied in an effort to determine the nature of the depressed PHA reactivity. The reduced response of DNA synthesis (thymidine incorporation) to PHA stimulation could not be attributed to a decreased viability of spleen lymphocytes from old mice in in vitro culture conditions, to different PHA dose requirements, or to longer periods of culture time for old mouse spleen cells to reach maximal activity. Culture of cells for 24-48 h prior to addition of PHA gave patterns of thymidine incorporation similar to those of freshly prepared spleen cells. The elimination of red blood cells by a brief hypotonic shock significantly increased thymidine incorporation in spleen lymphocytes from both yound and old mice.