Antigenic burden and serum IgG concentrations influence rituximab pharmacokinetics in rheumatoid arthritis patients.

AIMS: Rituximab is a monoclonal antibody directed against CD20, which is approved in rheumatoid arthritis (RA). This study aimed at assessing the influence of CD19+ cell counts as target-antigen amount, and of immunoglobulin G (IgG) serum concentrations on rituximab pharmacokinetics in RA patients. METHODS: In a cohort of 64 RA patients who had received repetitive courses of rituximab, the influence of CD19+ cell count, IgG serum concentration, body surface area, sex and disease activity score in 28 joints on rituximab pharmacokinetic parameters was assessed using a population pharmacokinetic analysis. RESULTS: A two-compartment model, with first-order distribution and elimination best described the data. The volume of distribution of central compartment and clearance of rituximab were estimated at 4.7 l and 0.56 l day-1 , respectively. Distribution and elimination half-lives were 0.9 days and 17.3 days, respectively. As expected, the central volume of distribution increased with body surface area (P = 0.012) and was higher in male than in female (P = 0.004). We found that the elimination rate constant (k10 ) increased with CD19+ count (P = 0.00022) and IgG concentration (P = 7.4 × 10-8 ), and that k10 decreased with time (P = 0.00015), partly explained by a change in target-antigen amount. CONCLUSIONS: The association between CD19+ count and k10 may be explained by target-mediated drug disposition, while the association between IgG serum concentration and k10 may be explained by a saturation of the neonatal Fc receptor at high IgG concentrations, resulting in decreased recycling of rituximab.

A highly stable, sensitive, regenerable and rapid immunoassay for detecting aflatoxin B1 in corn incorporating covalent AFB1 immobilization and a recombinant Fab antibody.

A highly robust immunoassay applicable for the detection of aflatoxin B1 (AFB1) using a Fab antibody fragment was developed. A key factor was the use of covalently immobilized AFB1 which allowed an almost three fold increase in sensitivity, reduced assay time and regeneration with retention of binding capacity. Various factors that might affect the sensitivity of the assay such as pH, organic solvents, storage stability and wash stringency were critically evaluated. It was also demonstrated that the assay was applicable for determination of AFB1 in corn samples at concentration within the European union regulatory limits.

Use of T-2 toxin-immobilized amine-activated beads as an efficient affinity purification matrix for the isolation of specific IgY.

An affinity purification method that isolates T-2 toxin-specific IgY utilizing a T-2-toxin-immobilized column was developed. The T-2 toxin was covalently coupled via a carbonyldiimidazole-activated hydroxyl functional group to amine-activated sepharose beads. The affinity-purified IgY was characterized by gel electrophoresis, fast protein liquid chromatography, enzyme-linked immunosorbant assay, surface plasmon resonance and mass spectrometry. A competitive inhibition ELISA (CI-ELISA) was performed using affinity-purified IgY with a T-2 toxin detection sensitivity of 30 ng/mL, which falls within the maximum permissible limit of 100 ng/mL. The cross reactivity of IgY towards deoxynivalenol, zearalenone, fumonisin B1 and HT-2 was significantly reduced after affinity purification. A surface plasmon resonance (SPR)-based inhibition assay was also applied for quantitative determination of T-2 toxin in spiked wheat samples. The results obtained indicate the feasibility of utilizing this IgY-based assay for the detection of T-2 toxin in food samples.