IL-6 mRNA expression by PMNs after cross-linking FcγRI or FcγRII. Purified PMNs were obtained from normal donors and IL-6 mRNA expression evaluated by RT-PCR. Data are presented for unstimulated PMNs (lane 1), PMNs after exposure to cross-linker (CL) alone (lane 2), and PMNs after exposure to (Fab′)₂32.2 (anti-FcγRI Ab) or Fab′ IV.3 (anti-FcγRII Ab) in the absence or presence of cross-linking antibody (lanes 3 through 6). RNA was reverse-transcribed and PCR-amplified using IL-6–specific primers as described in the text. RNA integrity was evaluated by using β-actin primers. The data presented are representative of four nearly identical experiments.