In vitro stimulation of peripheral blood mononuclear cells by phytohaemagglutinin A induces CD45RA expression on monocytes.

Following phytohaemagglutinin A stimulation, CD45RA positive monocytes increased from 12.2 +/- 8.9% to 63.5 +/- 8.8% (p < 0.001), without a significant change in cell surface antigen density. In contrast, HLA-DQ antigen, also expressed in 76.8 +/- 10.5% of the monocytes after PHA stimulation for 48 h, revealed a marked enhancement in fluorescence intensity (p < 0.001). This up-regulation is already evident in unstimulated cultures. The percentages of CD45RA and HLA-DQ positive monocytes were correlated (r = 0.80, p < 0.001), substantiating a previous clinical observation. CD45RA expression may probe activated mono/macrophages.