PCMCs were dissolved at 10 mg/ml in sodium citrate buffer [50 mM sodium citrate, 20 mM Tris, 1 mM EDTA, pH6.8]. The PCMC solution was diluted 1:3 v/v in carbonate coating buffer [15 mM Na2CO3, 30 mM NaHCO3, pH9.5] and serially diluted in a flat-bottom 96-well ELISA plate (MAXISorp, Nunc, UK). Plates were incubated overnight at 4 °C prior to washing 3 times in PBST. Non-specific binding was blocked by addition of 100 μl/well of block-B and incubation for 1 h at 37 °C. For BSA-containing PCMCs, block-G was used in place of block-B. After further washing, samples were incubated (2 h, 37 °C) with 50 μl/well of the
appropriate primary antibody [anti-DT selleck screening library (NIBSC, 1/1000), anti-CyaA* (in-house, 1/500)] or anti-BSA (Sigma, 1/1000)] diluted in the appropriate blocking buffer. After washing, 50 μl/well of peroxidase-conjugated secondary antibody (Sigma) diluted 1/1000 in the appropriate blocking buffer was added and plates incubated for 1.5 h at 37 °C. Plates were washed again and protein
binding was visualised using 50 μl/well of O-phenylene-diamine. After incubation for 10–15 min at rt, colour development was stopped with 3 M HCl and absorbance at 492 nm was measured. Protein loading onto PCMCs was quantified by comparison to a stock antigen standard curve. PARP inhibitor For SEM, dry PCMCs were gold-plated prior to visualisation with a JEOL6400 electron microscope operating at 6 kV. PCMCs were suspended at
10 mg/ml in 1.5 ml of either 0.1 mM sodium citrate (pH 6.0) or PBS and incubated at rt or 37 °C with gentle agitation. At intervals, the PCMC suspension was centrifuged for 1 min at 2400 × g and 1 ml of supernate removed to determine protein release. More buffer was then added to the pelleted PCMCs to readjust the volume to 1.5 ml and the incubation continued. Supernates were stored at −20 °C prior to quantification of protein release by through ELISA as described above. Soluble antigens were dissolved in sterile PBS containing 10% Al(OH)3 (A8222, Sigma), mixed thoroughly and incubated overnight at 4 °C. Adsorbed antigens were then used for immunisation. Groups of 8 inbred, female 6–8 week old NIH mice (Harlan, UK) were injected subcutaneously at days 0 and 28 with 0.5 ml volumes of the desired formulation or PBS as a control. Immediately prior to immunisation, the required doses of PCMCs were suspended in sterile PBS. Mice were sampled for sera at 28 d and 42 d post-immunisation, as described previously . All animal experiments were performed under UK Home Office License and in accordance with EU Directive 2010/63/EU. Antigen-specific IgG, IgG1 and IgG2a titres were determined using ELISA as described previously  with the use of block-G when determining anti-BSA responses. Geometric mean titres were calculated by comparison to reference sera. Murine monocyte/macrophage J774.