Electrochemical sensors based on immobilised cytochrome c or superoxide dismutase for the measurement of superoxide radical production by stimulated neutrophils are described. Cytochrome c was immobilised covalently at a surface-modified gold electrode and by passive adsorption to novel platinised activated carbon electrodes (PACE). The reoxidation of cytochrome c at the electrode surface upon reduction by superoxide was monitored using both xanthine/xanthine oxidase and stimulated neutrophils as sources of the free radical. In addition, bovine Cu/Zn superoxide dismutase was immobilised to PACE by passive adsorption and superoxide, generated by xanthine/xanthine oxidase, detected by oxidation of hydrogen peroxide produced by the enzymic dismutation of the superoxide radical. A biopsy needle probe electrode based on cytochrome c immobilised at PACE and suitable for continuous monitoring of free radical production was constructed and characterised.

SUMMARYAs elevated levels of glycated IgG have been detected in the plasma of patients with diabetes mellitus, a disease associated with increased susceptibility to infection, we have investigated whether glycation of MoAbs affects the kinetics and/or affinity of antigen binding. Three mouse MoAbs were incubated with 0-5 M glucose at pH 7-4 for 14-21 days at 37°C. Control MoAbs were incubated using identical conditions but with no added glucose. Using a surface plasmon resonance technique we found that glycation significantly increased the rate of dissociation (kdiss) of the antigen-antibody complex for all three MoAbs (P < 0*05, n = 4), but had no significant effect on the rate of association (kass). For one of the MoAbs, against human IgG (Fab), we also measured kdiS. by an alternative method utilizing radiolabelled antigen, which confirmed that glycation of the antibody significantly increases kdiss (P < 0001, n = 8). We also found using an ELISA-based method that glycation of the same MoAb significantly increased the equilibrium dissociation constant (Kd) (P < 0 05, n = 6). A significant increase in kd was observed after glycation using glucose concentrations consistent with those found in poorly controlled diabetics (P < 0 02, n = 5). We conclude that in vitro glycation can significantly lower the affinity of an antibody for its antigen, and significantly increases the rate of dissociation of the antigenantibody complex.

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