Objective: To investigate the roles of dendritic cells (DCs) in the pathogenesis of asthma.
Methods: (1) DCs were derived from peripheral blood monocytes of asthmatics with acute exacerbation (group A, n = 20), patients at remission (group B, n = 15) and healthy volunteers (group C, n = 10), and cultured using media supplemented with granulocyte-macrophage colony stimulation factors (GM-CSF), interleukin-4 (IL-4) and tumor necrosis factor-alpha (TNF-alpha). The antigen-uptaking function of the monocyte-derived DCs was evaluated by phagocytosis of fluorescence labeled ovalbumin (OVA), and their antigen-presenting function was determined by expression of membrane markers (MHC-II) and co-stimulatory molecules (CD(80) and CD(86)). The proliferation of T lymphocytes induced by DCs was assessed using autologous mixed T lymphocyte reaction. (2) The expression of MHC-II and CD(80) and CD(86) of DCs were determined from the bronchoalveolar lavage (BAL) of asthmatic rats. The effects of dexamethasone on the expression of these markers and molecules were studied. Twenty-four rats were divided into the experimental group (group D) and the control group (group E). In group D, rats were subdivided into two groups with 8 rats in each. One group (group D(2)) received pre-treatment with dexamethasone (10 mg/kg), and another group (group D(1)) did not received dexamethasone pre-treatment, while group E was matched with the experimental group with regard to both age and weight. The rats were sensitized and challenged with OVA, and BAL was obtained. (3) All the membrane markers and co-stimulatory molecules on the surface of DCs were determined using flow cytometric method.
Results: (1) The phagocytosis of fluorescence labeled OVA in group A was increased [(41 +/- 12)%] compared with those in group B [(29 +/- 10)%, P < 0.01] and group C [(29 +/- 10)%, P < 0.01]. The expression of MHC-II, CD(1alpha) and CD(80) on the surface of DCs was the highest in group A [(44 +/- 15)%, (32 +/- 11)% and (32 +/- 13)%, respectively] compared with those in group B [(22 +/- 10)%, (19 +/- 9)% and (19 +/- 10)%, all P < 0.01, respectively], as well as with those in group C [(18 +/- 12)%, (13 +/- 7)% and (14 +/- 7)%, all P < 0.01, respectively]. There was no statistical difference in the expression of CD(86) on the cell membrane in group A, group B and group C. In autologous mixed T lymphocyte reaction study, when DC/T ratio was 1/5, DCs had the highest ability in stimulating the proliferation of T lymphocytes in group A (stimulating index = 2.32 +/- 0.44) compared with those in group B (1.01 +/- 0.11, P < 0.01), and those in group C (1.62 +/- 0.27, P < 0.01). (2) The expression of MHC-II in BAL cells of asthmatic rats reached peak value at 6 h after challenge, (15.2 +/- 5.0)% in group D(1), and (2.0 +/- 1.0)% in group E, P < 0.01. The expression of CD(80) and CD(86) increased rapidly 2 h after challenge in group D(1) [(10.6 +/- 3.9)% and (7.5 +/- 3.8)%, respectively] compared with those in group E [(2.1 +/- 0.7)%, P < 0.01 and (1.7 +/- 0.7)%, P < 0.05, respectively]. The maximal inhibition effect of dexamethasone on the expression of MHC-II was at 10 h, (7.8 +/- 2.4)% in group D(1), and (2.8 +/- 1.5)% in group D(2), P < 0.01. The inhibition effect of dexamethasone on the expression of CD(80) and CD(86) was maximal at 24 h, (5.8 +/- 2.7)% and (5.5 +/- 1.5)% respectively in group D(1), and (2.8 +/- 1.1)% and (2.9 +/- 1.6)% respectively in group D(2), P < 0.05.
Conclusions: The antigen up-taking and presenting function of DCs were significantly enhanced in asthmatics at exacerbation and in a rat asthmatic model. Pretreatment with dexamethasone inhibited the function of DCs significantly in the animal model. The results suggest that DCs play important roles in antigen presentation in the pathogenesis of asthma, and the inhibition of glucocorticiod on DCs might be a critical mechanism in treatment of bronchial asthma.