The action of trypsin on human stored peripheral lymphocytes.

1. To assess the feasibility of using small lymphocytes from routinely refrigerated human blood for studies of surface biochemistry, the stored cells were compared with those from freshly drawn blood. The two were morphologically indistinguishable and gave similar mitotic responses to phytohaemagglutinin (PHA) and pokeweed mitogen (PWM). Furthermore, both sets gave an additive response when the two mitogens were present, indicating that the different (but possibly overlapping) lymphocytic populations which respond to PHA and PWM withstand storage equally well. 2. The stored lymphocytes were exposed to trypsin at concentrations up to 1 mg/ml for 10 minutes at 37°. They remained morphologically intact by both light and electron microscopy, and were undamaged as judged by exclusion of trypan blue and by release of label from Cr-tagged cells. 3. Exposure to trypsin at 0·1–1·0 mg/ml ablated the mitotic responses to PHA or PWM added to the lymphocytes immediately after the incubation with enzyme. However, the ability to respond to both mitogens was recovered during culture, suggesting that surface receptors for the mitogens had been removed by the enzyme but subsequently resynthesized. In the absence of mitogen the cells showed no mitotic response to trypsin.