It was found that IgA1 bound to MC with 12 106 binding-sites/cell, an affinity constant (Ka) of 23 106M?1 and a dissociation constant (Kd) of 44 10?7M. labelled with 125I. Binding capacity of aIgA1 to cultured main HMC was evaluated by a radioligand binding assay and the specificity of binding was determined by a competitive inhibition assay. Intracellular calcium release was analyzed by confocal analysis and phosphorylation of extracellular signal-regulated kinase (ERK) was determined by Western blot analysis. Switch of cell cycles was exhibited by circulation cytometry and HMC proliferation was evaluated by direct cell count. Expression of TGF- mRNA and production of supernatant fibronectin were tested by RT-PCR and indirect competitive ELISA, respectively. aIgA1 from both the patients with IgAN and normal controls bound to HMC in a dose-dependent, saturable manner, and was saturated at approximately 500 pmoles per 05 ml of aIgA1. aIgA1 from patients with IgAN, however, bound to HMC at a higher velocity and Scatchard analysis revealed a Kd of (889 21) 10?8m(43 12) 10?7m for aIgA1 from healthy controls (= 0026).The binding was specific because it was only inhibited by unlabelled Mono-IgA1 (mIgA1) and not by serum albumin or IgG. aIgA1 from patients with IgAN could induce release of intracellular calcium, phosphorylation of ERK, DNA synthesis, proliferation of HMC, expression of TGF-mRNA and secretion of fibronectin in HMC in a similar time-dependent manner as aIgA1 from healthy controls, but the effects were much stronger and the durations AG-120 were much longer ( 005, respectively). We conclude that aIgA1 from patients with IgAN has a higher binding capacity to HMC and stronger biological effects than aIgA1 from healthy controls. This suggests that direct conversation between IgA1 and HMC and subsequential pathophysiological responses may play AG-120 an important role in the pathogenesis for IgAN. that IgA1 with reduced galactosylation decreases the ability of liver to eliminate the abundant circulating IgA1, resulting in accumulation of IgA1 in blood and self-aggregation, favouring the deposition of macromolecular IgA1 in glomerular mesangium [15,16]. pIgA1 has been demonstrated in protein eluates of biopsy specimens from IgAN patients [17,18] and a study of three kidneys indicates that mesangial pIgA1 is usually enriched for the Gal-deficient O-glycosylation pattern seen in serum IgA1 [19], strongly suggesting that this O-glycan abnormality is indeed directly implicated in mesangial IgA deposition. Recently, increasing evidences have exhibited that IgA1, isolated from Rabbit polyclonal to AASS healthy individuals, binds to MC in a dose dependent and saturable manner, and the binding is usually specific for IgA1 because only IgA1 Fc fragments could inhibit the binding whereas albumin, IgG, IgM, and IgA1 F(ab) fragments could not [20C22]. It was found that IgA1 bound to MC with 12 106 binding-sites/cell, an affinity constant (Ka) of 23 106M?1 and a dissociation constant AG-120 (Kd) of 44 10?7M. Addition of various cytokines experienced no significant influence on Ka, but increased the number of binding sites/cell compared with unstimulated cells [23]. Moreover, binding of IgA1 to MC could induce intracellular transmission transduction [22, 24, 25] and up-regulation of the secretion of pro-inflammatory cytokines, such as IL-6, TNF-, etc. [24,26C28]. Therefore, it has been suggested that IgA1 binding to MC is usually via a specific Fc receptor on MC and the conversation between IgA1 and the MC is usually one important aspect in the pathogenesis of IgAN. Leung for 10 min and protein concentration in supernatants was measured by the Bradford method [32] using BSA as the standard. Samples of 15 mg (for total ERK) or 30 mg (for phosphorylated ERK) were electrophoresed and transferred to polyvinylidene difluoride membranes. Detection of total ERK and phosphorylated ERK proteins was accomplished by a first incubation with 1 : 2000 dilution of rabbit anti-human ERK and mouse anti-human phosphoralated ERK (Santa Cruz Biotechnology), respectively, and followed by a 1 : 5000 dilution of horseradish peroxidase-conjugated secondary antibodies (Amersham, Buckinghamshire, UK). Membranes were washed and exposed to Kodak X-Omat S films using an ECL chemiluminescence kit (Amersham, Buckinghamshire, UK)..