Confocal analysis of PLCγ1 expression at the external leaflet of the plasma membrane in human T lymphocytes. (A) Unstimulated cell (increments of 0.85 μm in z-axis; cell size, 8 μm); (B) PHA-stimulated cell (increments of 0.9 μm in z-axis; cell size, 17 μm); (C) PHA-stimulated cell incubated for 90 minutes with interferon beta (increments of 0.75 μm in z-axis; cell size, 14 μm). (D) PHA-stimulated cell incubated for 24 hours with interferon beta (increments of 0.54 μm in z-axis; cell size, 10 μm); (E) cell labeled with anti-Leu-5b MoAb (CD 2), used as an internal control (increments of 0.56 μm in z-axis; cell size, 11 μm). Note that the membrane labeling evident in resting lymphocytes became weaker in PHA-stimulated cells, and again was strongly detectable after addition of interferon. As internal controls, cells were incubated with anti-Leu-5b MoAb, a T-lymphocyte surface marker, which strongly labeled the membranes (Fig 2E), while the reactions performed in the absence of the primary antibody yielded consistently negative results. Results obtained by incubating lymphocytes with anti-STAT 91/84 protein as an intracellular marker (to check membrane integrity) and with anti-PLC β and δ isoforms did not disclose any FITC membrane labeling.