Src family PTK activity is required for induction of IL-1ra and IL-8 in THP-1 cells after cross-linking of FcαR by huIgA-adsorbed NC particles. THP-1 cells (3 × 10⁶cells/mL/well) were stimulated for 24 hours with huIgA adsorbed to nitrocellulose particles (IgA-NC); parallel cultures were incubated in the presence of corresponding concentrations of soluble huIgA or BSA-adsorbed nitrocellulose particles (NC). In (A) and (B), cells were cultured in complete medium (Med) or in complete medium containing PMB (final concentration, 10 μg/mL) or PP1 (final concentration, 100 μmol/L). In (C), THP-1 cells were stimulated for 24 hours with huIgA adsorbed to NC particles (final concentration of huIgA, 100 μg/mL) in the presence of PP1 at the indicated concentrations. Release of IL-1ra and IL-8 was examined in cell-free supernatants as described in Materials and Methods. Results are expressed as nanograms per milliliter (mean ± SEM of 3 experiments [A] or 6 experiments [B]) or (C) as a percentage of control (mean ± SEM of 3 experiments) relative to the cytokine release observed in cells stimulated with huIgA-particles in the absence of PP1 (cytokine release, in nanograms per milliliter, mean ± SEM: IL-1ra, 7.99 ± 0.84; IL-8, 1.41 ± 0.04). (*) Statistically significant difference between cultures stimulated with huIgA-NC and cells cultured in the presence of huIgA or NC alone (both in the presence or absence of polymyxin B, 10 μg/mL;P<0.05, Newman-Keuls multiple comparisons test; P = .004, analysis of variance). (#) Statistically significant difference as compared with cultures containing soluble huIgA or NC particles alone (P < .01, Kruskal-Wallis test for comparison of more then two samples). (x) Statistically significant difference as compared with cells stimulated with huIgA adsorbed to NC particles in the absence of PP1 (P = .01, Mann-Whitney U test). (+) Statistically significant inhibition of cytokine release after stimulation with huIgA adsorbed to NC particles (P < .025, Student's t-test for paired samples).