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Background: Airway smooth muscle proliferation plays an important role in airway remodeling in asthma. But little is known about the intracellular signal pathway in the airway smooth muscle cell proliferation in asthma. The objective of this paper is to investigate the contribution of protein kinase C (PKC) and its alpha isoform to passively sensitized human airway smooth muscle cells (HASMCs) proliferation., Methods: HASMCs in culture were passively sensitized with 10% serum from asthmatic patients, with non-asthmatic human serum treated HASMCs used as the control. The proliferation of HASMCs was examined by cell cycle analysis, 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazoliumbromide (MTT) colorimetric assay and proliferating cell nuclear antigen (PCNA) immunofluorescence staining. The effect of PKC agonist phorbol 12-myristate 13-acetate (PMA) and PKC inhibitor Ro-31-8220 on the proliferation of HASMCs exposed to human asthmatic serum and non-asthmatic control serum was also examined by the same methods. The protein and mRNA expression of PKC-alpha in passively sensitized HASMCs were detected by immunofluorescence staining and reverse transcription-polymerase chain reaction., Results: The percentage of S phase, absorbance (value A) and the positive percentage of PCNA protein expression in HASMCs passively sensitized with asthmatic serum were (16.30 +/- 2.68)%, 0.430 +/- 0.060 and (63.4 +/- 7.4)% respectively, which were significantly increased compared with HASMCs treated with control serum [(10.01 +/- 1.38)%, 0.328 +/- 0.034 and (37.2 +/- 4.8)%, respectively] (P < 0.05). After HASMCs were passively sensitized with asthmatic serum, they were treated with PMA, the percentage of S phase, value A and the positive percentage of PCNA protein expression were (20.33 +/- 3.39)%, 0.542 +/- 0.065 and (76.0 +/- 8.7)% respectively, which were significantly increased compared with asthmatic serum sensitized HASMCs without PMA(P < 0.05). After HASMCs passively sensitized with asthmatic serum were treated with Ro-31-8220, the percentage of S phase, value A and the positive percentage of PCNA protein expression were (11.21 +/- 1.56)%, 0.331 +/- 0.047 and (38.8 +/- 6.0)% respectively, which were significantly decreased compared with asthmatic serum sensitized HASMCs without Ro-31-8220 (P < 0.05). The relative ratio of value A of PKC-alpha mRNA and the positive percentage of PKC-alpha protein expression in passively sensitized HASMCs were 1.23 +/- 0.10 and (61.1 +/- 9.4)% respectively, which were significantly increased compared with HASMCs treated with control serum [1.05 +/- 0.09 and (34.9 +/- 6.7)%, respectively] (P < 0.05)., Conclusions: The proliferation of HASMCs passively sensitized with human asthmatic serum is increased. PKC and its alpha isoform may contribute to this proliferation.