Variability in detection and quantification of interferon ß-1b-induced neutralizing antibodies.

BACKGROUND: Interferon-beta (IFNB) therapy for multiple sclerosis can lead to the induction of neutralizing antibodies (NAbs) against IFNB. Various methods are used for detection and quantification of NAbs. METHODS: Blood samples from 125 IFNB-1b-treated patients, which were tested NAb negative or NAb positive after conclusion of a clinical study, were retested three years after first being assessed in four different laboratories that offer routine NAb testing to practicing neurologists. The myxovirus protein A (MxA) induction assay, the cytopathic effect (CPE) assay (two laboratories), or the luciferase assay were used. Intra- and inter-laboratory agreement between assays with respect to NAb detection and NAb titer quantification were evaluated. RESULTS: High agreement for NAb detection (kappa coefficient, 0.86) and for titer levels was observed for the intra-laboratory comparison in the laboratory using the MxA induction assay performed three years ago and now. A similarly high agreement for NAb detection (kappa coefficient, 0.87) and for titer quantification was noted for the MxA assay of this laboratory with one of two laboratories using the CPE assay. All other inter-laboratory comparisons showed kappa values between 0.57 and 0.68 and remarkable differences in individual titer levels. CONCLUSIONS: There are considerable differences in the detection and quantification of IFNB-induced NAbs among laboratories offering NAb testing for clinical practice using different assay methods. It is important that these differences are considered when interpreting NAb results for clinical decision-making and when developing general recommendations for potentially clinically meaningful NAb titer levels.

[Comparison of antimicrobial and bactericidal activities and postantibiotic effects of macrolides antibiotics against clinical isolates, and examination of shape alteration by scanning electron microscope].

We examined antibacterial activities of 4 kinds of macrolides (MLs), erythromycin (EM), clarithromycin (CAM), azithromycin (AZM) and rokitamycin (RKM), against 4 bacterial species of clinical strains isolated in 2004. Bacterial isolates used were 51 strains of methicillin-susceptible Staphylococcus aureus (MSSA), 20 of Streptococcus pyogenes, 68 of Streptococcus agalactiae, and 120 of Streptococcus pneumoniae. Macrolide resistance genes, ermB and mefE, in macrolide-resistant S. pyogenes and S. agalactiae, and all of pneumococci were analyzed by PCR. Antimicrobial activities against macrolide-susceptible MSSA of EM and CAM, were more potent than those of RKM. By contrast, against S. pneumoniae, RKM was more effective than EM, CAM and AZM. Against S. pyogenes and S. agalactiae, 4 antibiotics showed similar antimicrobial activities. Twelve, 1 and 2 strains of MSSA, S. pyogenes and S. agalactiae, respectively, were resistant to EM, CAM and AZM, whereas RKM was active to almost, but not quite, of them. Among 120 strains of S. pneumoniae, 76 (63.3%) were resistant to EM (MIC; > or = 0.5 microg/mL), and 23, 15 and 28 strains were highly resistant (MIC; > 128 microg/mL) to EM, CAM and AZM, respectively. By contrast, for RKM, there were far fewer resistant strains, and there was no highly resistant strain. PCR analyses of macrolide-resistant genes revealed that 1 resistant strain of S. pyogenes and 2 of S. agalactiae carried mefE and ermB, respectively. In the case of S. pneumoniae, 59, 19 and 5 strains, respectively, carried ermB, mefE and both ermB and mefe. We also studied about bactericidal activities and postantibiotic effects (PAE) of MLs using macrolide-susceptible, and ermB- and mefE-carrying S. pneumoniae, and observed morphological alterations of the strains treated with the drugs by a scanning electron microscope. It was demonstrated that RKM had superior bactericidal activities and PAE than other 3 drugs, and potent destructive effects to all of 3 strains.