The OKT3 Antibody Response Study: a multicentre study of human anti-mouse antibody (HAMA) production following OKT3 use in solid organ transplantation

Human anti-murine antibody titres following patient exposure to the monoclonal antibody Orthoclone OKT3 (muromonab-CD3) are determined by laboratories using diverse analytical methods which are not standardized and whose concordance is not established. A multicentre study group therefore compared testing for IgG anti-OKT3 antibody among seven laboratories. A set of 270 sera was obtained from 30 heart, 30 kidney and 30 liver transplant recipients with no previous exposure to OKT3 who were receiving OKT3 for induction immunosuppression. Sera were collected from each patient prior to and at 24 +/- 2 days and 31 +/- 2 days following initial OKT3 exposure. Identical aliquots of all 270 sera were tested for IgG anti-OKT3 antibody by each laboratory. In addition, the limit of detection of each laboratory's method was estimated by titration of an affinity-purified IgG anti-OKT3 reference material of known concentration. Anti-OKT3 antibody formation differed greatly among the three organ groups. Cardiac patients demonstrated the least sensitization and almost exclusively lower titres, while kidney recipients had more frequent and higher titre antibody formation. Liver recipients yielded the highest sensitization rate and the most frequent high titre sera. Importantly, the seven laboratories differed widely in the number of pretreatment sera reported as positive (ranging from 0% to 41% among laboratories), the number of post-OKT3 sera reported as positive (17-63%), the number of post-OKT3 samples with titre > or = 1000 (2-31%), and the number of patients sensitized 19-69%). Concordance among laboratories was highly variable, with interlaboratory agreement ranging from 38% to 83% on the sample titres assigned to 180 post-OKT3 sera. Many of the discordant results were consistent with differences in the limit of detection of the analytical methods, which ranged from 0.19 microgram/ml to > or = 15 micrograms/ml, a nearly 100-fold difference among laboratories. This study demonstrated the presence of both good concordance and significant discordance among laboratories in determining human anti-mouse antibody titres, and demonstrated that common titre categories (100, 1000, 10,000) were not equivalent among laboratories. The level of concordance among methods should be considered when comparing anti-OKT3 antibody results from different centres and their correlation with clinical events. Universal comparative testing, patterned after proficiency testing programmes, is needed to assess differences among laboratories and to bring uniformity and a sound interpretative basis to this field of testing.     

Deoxyribonucleic acid vaccines encoding antigens with rapid proteasome-dependent degradation are highly efficient inducers of cytolytic T lymphocytes

We generated plasmid expression vectors encoding ubiquitin and beta-galactosidase (beta-gal) with different intervening amino acids, allowing for the production of processed protein products that have either stabilizing or destabilizing residues at their N-termini. P815 cells transfected with plasmids encoding beta-gal with a destabilizing N-terminus did not have detectable expression beta-gal unless they were treated with inhibitors specific for the proteasome. Inhibitors of other proteolysis pathways had no such effect. Nevertheless, transfectants expressing beta-gal with different amino acid residues were equally sensitive to cytolysis by a CTL clone specific for a beta-gal peptide presented in the context of H-2Ld. In contrast to vectors encoding native beta-gal, plasmid vectors encoding beta-gal with a destabilizing residue did not induce detectable anti-beta-gal Abs when injected into skeletal muscle of BALB/c mice. However, such vectors were significantly more effective than vectors encoding native beta-gal or beta-gal with a stabilizing residue in stimulating CTL specific for P13.2, a lacZ transfectant of P815. We conclude that incorporation of strategies that enhance proteasome-dependent degradation may generate DNA vaccines that are more effective in inducing cellular immunity against targeted Ags.     

Porphyromonas (Bacteroides) endodontalis: its role in endodontal infections

Porphyromonas endodontalis (formerly Bacteroides endodontalis) is a black-pigmented anaerobic Gram-negative rod which is associated with endodontal infections. It has been isolated from infected dental root canals and submucous abscesses of endodontal origin. The presence of P. endodontalis in infected dental root canals has been correlated with symptoms of an acute infection. It is occasionally found on oral mucous membranes and periodontal pockets. P. endodontalis has shown relatively low virulence in experimental monoinfections. In anaerobic mixed infections it can play an essential role. Differences in virulence between strains have been related to capsular material. On the basis of different types of capsules, three serotypes have been described. P. endodontalis is sensitive to a wide range of antibiotics, including the penicillins, the tetracyclines, and metronidazole.     

A set of electrophoretic molecular markers for strain typing and population genetic studies of Histoplasma capsulatum

A set of eleven biallelic and three multiallelic molecular markers have been developed to analyze populations of Histoplasma capsulatum. All markers are amplified by polymerase chain reaction (PCR) and can be readily scored using minimal amounts of template DNA. The 11 biallelic loci have polymorphic restriction endonuclease sites or small insertions or deletions which may be assessed by agarose gel electrophoresis. These markers are inherited in an unambiguous manner and are ideal for assessing structure and gene flow within US populations of H. capsulatum, but are monomorphic in non-US populations. Both length and sequence variation are present in the multiallelic loci, which can be scored by direct sequencing, polyacrylamide gel electrophoresis, or single-strand conformation polymorphism (SSCP): As they are hypervariable, the multiallelic loci can be used to type isolates and to assess the level of genetic variation within populations. Preliminary results indicate that the three multiallelic markers presented are sufficient to distinguish isolates at the individual level and are polymorphic in both US and non-US populations. This collection of molecular markers will be a useful tool in population and epidemiology studies of H. capsulatum.     

An exemplar-based random walk model of speeded classification

The authors propose and test an exemplar-based random walk model for predicting response times in tasks of speeded, multidimensional perceptual classification. The model combines elements of R. M. Nosofsky's (1986) generalized context model of categorization and G. D. Logan's (1988) instance-based model of automaticity. In the model, exemplars race among one another to be retrieved from memory, with rates determined by their similarity to test items. The retrieved exemplars provide incremental information that enters into a random walk process for making classification decisions. The model predicts correctly effects of within- and between-categories similarity, individual-object familiarity, and extended practice on classification response times. It also builds bridges between the domains of categorization and automaticity.