CYTOKINE EXPRESSION BY HIGH-DENSITY HUMAN-LYMPHOCYTES

T lymphocytes spend much of the time as small non-cycling cells. To de termine the pattern of cytokine expression in such resting cells, they were purified from human peripheral blood mononuclear cells (PBMC) on the basis of high buoyant density. The cells were stimulated and cyto kine mRNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Expression of interleukin-2 (IL-2), IL-3 and interferon-gamma (IFN-gamma) was similar in high-density lymphocytes a nd in unfractionated PBMC. In contrast, the high-density lymphocytes e xpressed less IL-4 than PBMC, and little or no IL-5. Because a substan tial minority of the high-density lymphocytes was CD45RO(+), the prese nce of this marker was not an indicator of the ability to express IL-4 and IL-5. In the high-density lymphocytes, IFN-gamma expression was c onfined to the CD45RO(+) fraction, whereas IL-2 was expressed by both CD45RO(+) and CD45RO(-) subsets. To assess whether high-density lympho cytes could give rise to cells with a broader range of inducible cytok ine expression, they were activated and then restimulated between 10 a nd 22 days of culture. Cells derived from both the CD45RO(+) and CD45R O(-) fractions of high-density lymphocytes expressed IL-5 after restim ulation. Thus the high-density lymphocyte population has the potential to acquire a broader range of inducible cytokine expression.