Artificial neural networks can distinguish novice and expert strategies during complex problem solving

OBJECTIVE

To determine whether expert problem-solving strategies can be identified within a large number of student performances of complex medical diagnostic simulations.

METHODS

Self-organizing artificial neural networks were trained to categorize the performances of infectious disease subspecialists on six computer-based clinical diagnostic simulation that used the sequence of diagnostic tests requested as the input data. Six hundred seventy-six student solutions to these problems were presented to these trained neural networks to determine which, if any, of the student solutions represented those of the experts.

RESULTS

For each simulation, the expert performances clustered around one dominant output neurode, indicating that there were common problem-specific features associated with the experts' problem-solving performances. When the performances of students who also made correct problem diagnoses were tested on these expert-trained neural networks, 17% were classified as representing expert strategies, indicating that expert performance was a somewhat rare and inconsistent occurrence among the students.

CONCLUSIONS

The ability to identify a small number of expert-like strategies within a large body of student performances may provide an opportunity to study the dynamics of complex learning at both individual and population levels as well as the emergence of medical diagnostic expertise.

A study of public health nursing directors in state health departments

Public health nurses make up the largest single category of public health manpower, but confusion over where and how public health nurses should function continues. The purposes of this study were to describe the current structure of public health nursing in state health departments in the United States, and to note whether this structure had changed over the last 5 years. Data were collected through a survey sent to each of the 50 U.S. State Health Departments. Forty-eight percent of the 50 states responded to the survey. From the results, we can conclude that there is currently no uniform description of what states expect of their state nurse directors, even though these individuals lead the largest portion of the public health workforce. The public and the public health system place a large, but often unwritten and unspoken, expectation on public health nurse leaders, but in recent years erosion has occurred in public health nursing in many states. Public health nursing is well positioned to provide leadership under health care reform. The challenge now facing public health nursing leaders is to maintain or create the infrastructure, as well as the organizational culture, to maximize these opportunities.

A random-effects model for analysis of infectious disease final-state data

Ball (1986, Advances in Applied Probability 18, 289-310) presented an extension to the "General Epidemic Model" in which an individual's (random) infectious period could have any distribution whose Laplace transform could be specified. This paper describes the fitting of Ball's model to data on the final state of infection within households, and gives an intuitive mathematical derivation of the corresponding likelihood function. We extend the model in several ways, including an extension to allow for random-effects heterogeneity in disease transmission rate between individuals. We give an algorithm for the efficient numerical computation of maximum likelihood estimators of the transmission rates, and describe the assessment of goodness of model fit. The methodology is illustrated with recent survey data on outbreaks of Shigella sonnei in 102 households in Manchester, UK. The results are consistent with previous anecdotal evidence of the infectiousness and susceptibility of individuals within households as a function of age and sex.

Prevalence and distribution of bacteriophage phi Aa DNA in strains of Actinobacillus actinomycetemcomitans

phi Aa is a bacteriophage that was originally isolated by induction of a lysogenic strain of the oral bacterium Actinobacillus actinomycetemcomitans. Since the discovery of phage phi Aa, additional phages infecting several other strains of A. actinomycetemcomitans have been identified. To determine the prevalence of phi Aa or phi Aa-related temperate phages in this species, a phi Aa-specific DNA probe was prepared to screen for homologous sequences among 42 strains of A. actinomycetemcomitans. Fourteen (33%) of the 42 strains examined contained DNA sequences that hybridized with the phage phi Aa probe. A bacteriophage designated phi Aa33384 was isolated by induction from one of the strains (ATCC 33384) that contained a sequence that hybridized with the phi Aa probe. The phi Aa probe hybridized with the DNA extracted from bacteriophage phi Aa33384. The distribution of the phage phi Aa sequence among A. actinomycetemcomitans serotypes was 5/13 (38%) of the serotype a strains, 0/16 (0%) of the serotype b strains, and 9/13 (69%) of the serotype c strains. The results of this investigation suggest that the target sequence prepared from the phage phi Aa genome is fairly common in the A. actinomycetemcomitans chromosome, and that the sequence is distributed among the A. actinomycetemcomitans serotypes in a seemingly nonrandom manner.

Artificial neural network comparison of expert and novice problem-solving strategies

The successful strategies of second-year medical students were electronically captured from computer-based simulations in immunology and infectious disease and were used to train artificial neural networks for the rapid classification of subsequent students' and experts' strategies on these problems. Such networks could categorize problem solutions of other students as successful or nonsuccessful > 85% of the time. These neural networks, however, performed poorly (as low as 13%) when classifying experienced immunologists' or internists' successful performances, suggesting an ability to distinguish between novice and expert strategies. The neural networks also identified a group of students who framed the infectious disease problems correctly, but had difficulty discriminating between differential diagnoses.

Conjugal transfer of broad-host-range incompatibility group P and Q plasmids from Escherichia coli to Actinobacillus actinomycetemcomitans

The first example of conjugal transfer of DNA from Escherichia coli to the periodontal pathogen Actinobacillus actinomycetemcomitans is presented. Derivatives of the incompatibility group P (IncP) plasmid RK2 successfully transferred from an E. coli donor to an A. actinomycetemcomitans recipient. The resulting A. actinomycetemcomitans transconjugants transferred the plasmids back to E. coli recipients. The IncP transfer functions were also used in trans to mobilize the IncQ plasmid pBK1 from E. coli to A. actinomycetemcomitans. The IncP and IncQ plasmids both transferred into A. actinomycetemcomitans at high frequencies (0.3 to 0.5 transconjugants per donor) and showed no gross deletions, insertions, or rearrangements. Determinations of MICs of various antibiotics for the A. actinomycetemcomitans transconjugant strains demonstrated the expression of ampicillin, chloramphenicol, and kanamycin resistance determinants.

Artificial neural networks as adjuncts for assessing medical students' problem solving performances on computer-based simulations

Artificial neural networks were trained by supervised learning to recognize the test selection patterns associated with students' successful solutions to seven immunology computer-based simulations. New test selection patterns evaluated by the trained neural network were correctly classified as successful or unsuccessful solutions to the problem > 90% of the time. The examination of the neural networks output weights after each test selection revealed a progressive and selective increase for the relevant problem suggesting that a successful solution is represented by the neural network as the accumulation of relevant tests. Unsuccessful problem solutions were classified by the neural network software into two patterns of students performance. The first pattern was characterized by low neural network output weights for all seven problems reflecting extensive searching and lack of recognition of relevant information. In the second pattern, the output weights from the neural network were biased toward one of the remaining six incorrect problems suggesting that the student misrepresented the current problem as an instance of a previous problem. Finally, neural network analysis could detect cases where the students switched hypotheses during the problem solving exercises.

Identification of Actinobacillus actinomycetemcomitans: polymerase chain reaction amplification of lktA-specific sequences

Actinobacillus actinomycetemcomitans has been strongly implicated in the etiology of localized juvenile periodontitis. Techniques used in the identification of this periodontal pathogen include cultural, biochemical, immunological and DNA hybridization analysis. In this study, we report the use of polymerase chain reaction (PCR) to amplify unique sequences of A. actinomycetemcomitans. Specific oligonucleotide primers LKT2 and LKT3 were designed to hybridize to the A. actinomycetemcomitans lktA gene, which encodes leukotoxin, a putative A. actinomycetemcomitans virulence factor. The LKT2 and LKT3 primers amplified lktA-specific sequences from all 12 A. actinomycetemcomitans strains tested. In another set of experiments, 13 other bacterial species, most of which are normal residents of the oral cavity, were tested with these primers. These PCR amplifications also contained 2 additional primers, RRN4 and RRN5, which served as positive controls; RRN4 and RRN5 were designed to amplify specific sequences of eubacterial 16S ribosomal DNA (rDNA). PCR amplifications of all bacterial species tested, including A. actinomycetemcomitans, yielded 16S rDNA-specific DNA fragments. Furthermore, each bacterial species tested, with the exception of A. actinomycetemcomitans, failed to amplify lktA sequences. The LKT and RRN primers were used in further PCR experiments to detect A. actinomycetemcomitans directly from gingival fluid samples. The results clearly demonstrate the simplicity, rapidity, specificity and accuracy of the LKT primers in the identification of A. actinomycetemcomitans.

Characterization and physical mapping of the genome of bacteriophage phi Aa from Actinobacillus actinomycetemcomitans

The size, configuration and restriction map of Actinobacillus actinomycetemcomitans bacteriophage phi Aa DNA was determined by means of restriction endonuclease analysis. Digestion of the phi Aa DNA with restriction enzymes Hind III, Eco RI and Sal I produced 6, 5, and 4 fragments, respectively. Based upon the sum of the sizes of the restriction fragments of these enzymes, the DNA was estimated to be 47.2 kilobase pairs in length. A restriction map was constructed using Hind III and Sal I. Incubation with exonuclease Bal 31 for increasing lengths of time resulted in progressive hydrolysis of the DNA, as expected for a linear molecule. No sub-molar fragments or diffuse bands were observed in the agarose gels of the restriction endonuclease digests of the phi Aa DNA. Attempts at ligating the ends of the DNA were consistently unsuccessful. Therefore, we found no evidence for cohesive ends, a circular permutation of the genome or for headful packaging mechanism from a concatameric DNA precursor.

Inhibition of B cell proliferation by antisense DNA to both alpha and beta forms of Fc epsilon R II

Epstein-Barr Virus (EBV) infection activates B lymphocyte proliferation through partially understood mechanisms, resulting in phenotypic changes, including the appearance of new antigens. One such antigen is Fc epsilon R II/CD-23 which may be relevant for B cell proliferation. We have used anti-sense oligonucleotides to study the importance of the two forms of this molecule for proliferation in the EBV-transformed, Fc epsilon R II +ve lymphoblastoid B cell line, RPMI 8866. Anti-sense oligodeoxynucleotides were generated to the two forms of Fc epsilon R II; Fc epsilon R IIa (alpha) and IIb (beta) which differ only in their intracytoplasmic domains. Addition of increasing concentrations of anti-sense oligonucleotides, ranging from 1 to 30 microM, significantly decreased cellular proliferation as measured by the incorporation of [3H]thymidine (inhibition range 8-88%). Optimum inhibition of cellular proliferation was apparent at 15 microM concentration of both anti-sense Fc epsilon R IIa and IIb (Fc epsilon R IIa, mean +/- SE = 75 +/- 7% inhibition, p less than 0.001; Fc epsilon R IIb, mean +/- SE = 71 +/- 7% inhibition, p less than 0.001). Anti-sense oligonucleotides complementary to the common part of Fc epsilon R II resulted in a similar inhibition of proliferation. Sense oligonucleotides did not induce significant inhibition. Preincubation of sense and anti-sense oligonucleotides resulted in an abrogation of proliferation inhibition. Moreover, none of these oligonucleotides had any effect on a Fc epsilon R II -ve cell line. Incubation with both anti-sense IIa and IIb resulted in additive, but not synergistic inhibition of proliferation. Addition of soluble Fc epsilon R II did not reverse inhibition of proliferation, suggesting that membrane-bound or intracellular rather than soluble Fc epsilon R II was important for the induced proliferation. Analysis of cell surface expression for Fc epsilon II indicated that while there was a pronounced effect on cell number following incubation with anti-sense oligonucleotides, surface expression of Fc epsilon R II was consistent as measured over different time points. PCR analysis revealed that while most cells expressed either the alpha or the beta form of Fc epsilon R II, EBV-transformed cell lines, particularly RPMI 8866, were found to express both alpha and beta forms simultaneously. This may constitute a mechanism whereby EBV infection confers an immortal state to the cell, resulting in its uncontrolled proliferation. Cell lines expressing only one receptor form, either alpha or beta, were unaffected after incubation with anti-sense oligonucleotides.(ABSTRACT TRUNCATED AT 400 WORDS)

Can artificial neural networks provide an "expert's" view of medical students performances on computer based simulations?

Artificial neural networks were trained to recognize the test selection patterns of students' successful solutions to seven immunology computer based simulations. When new student's test selections were presented to the trained neural network, their problem solutions were correctly classified as successful or non-successful > 90% of the time. Examination of the neural networks output weights after each test selection revealed a progressive increase for the relevant problem suggesting that a successful solution was represented by the neural network as the accumulation of relevant tests. Unsuccessful problem solutions revealed two patterns of students performances. The first pattern was characterized by low neural network output weights for all seven problems reflecting extensive searching and lack of recognition of relevant information. In the second pattern, the output weights from the neural network were biased towards one of the remaining six incorrect problems suggesting that the student mis-represented the current problem as an instance of a previous problem.

In vitro regulation of B cell differentiation by interleukin-6 and soluble CD23 in systemic lupus erythematosus B cell subpopulations and antigen-induced normal B cells

Polyreactive systemic lupus erythematosus (SLE) B cells were compared with antigen-induced SLE and normal B cells for their interleukin-6 (IL-6) and soluble CD23 requirements. Unlike normal B cells, secretion of antibody by SLE B cells in serum-free medium was not enhanced by exogenous IL-6. Anti-IL-6 antibodies inhibited immunoglobulin production in cultures of normal and SLE B cells, which suggests that IL-6 is required for B cell differentiation. SLE culture supernatants had elevated levels of IL-6, which explains the poor response of the SLE cells to exogenous IL-6. Soluble CD23 enhanced the responses of cells from normal subjects and SLE patients.

Solving the problem of how medical students solve problems

Although gathering and processing information are essential to medical problem solving, little is known about what strategies students use to gather information or how they use their cognitive skills to solve problems. We have developed computer-based problem-solving exercises in immunology to determine how students gather and process information. Graphic representations of students' search paths through different problems were developed to visualize how organized and focused their knowledge was, how well their organization related to critical concepts in immunology, where serious misconceptions (confusion or erroneous models) occurred, and whether proper knowledge links between conceptual domains existed. With rapid generation and interpretation of information on patterns and difficulties in problem solving, it should become possible to develop a specific and personal approach to each student's educational needs.

Interleukin 6 is essential for antibody secretion by human in vivo antigen-induced lymphoblastoid B cells

In vivo immunization of normal subjects with a variety of antigens generates circulating lymphoblastoid (LB) B cells, which in vitro spontaneously secrete significant levels of specific antibody. Since activation and initial differentiation of these cells occurs in vivo, they provide a useful model for the study of the later stages of B cell maturation. In the present study, we investigated the requirement of interleukin 6 (IL-6) for the "spontaneous" in vitro production of IgG-Tet by LB B cells. Addition of IL-6 to cultures of LB B cells in medium supplemented with 10% fetal calf serum failed to increase the levels of IgG-Tet produced in vitro. However, addition of anti-IL-6 antibodies decreased IgG-Tet production as much as 70%, and this inhibition could be reversed by the addition of IL-6. LB B cells cultured in serum-free medium in order to restrict endogenous IL-6 production secreted only low levels of antibody, unless exogenous IL-6 was added. Addition of 2.5 units/ml of IL-6 to serum-free cultures induced an increase in IgG-Tet secretion nearly comparable to that seen in cultures supplied with serum. The magnitude of the increase in IgG-Tet secretion in response to exogenous IL-6 was inversely related to the number of cells in culture, which was due in part to increased endogenous IL-6 production in cultures with higher cell concentrations. Experiments including hydroxyurea in serum-free cultures indicated that IL-6-dependent enhancement of LB B cells' IgG-Tet secretion was not primarily mediated by cell growth. These observations suggest that in vivo generated LB B cells are not totally committed to antibody secretion, and that IL-6 is essential for in vivo antigen-induced LB B cells to reach the antibody-secreting stage.

Soluble CD23 containing B cell supernatants induce IgE from peripheral blood B-lymphocytes and costimulate with interleukin-4 in induction of IgE

The role of soluble fragments of CD23 and their relationship to interleukin-4 (IL-4) in the in vitro production of IgE by normal human peripheral blood mononuclear cells was examined. Most donors' cells were induced to produce IgE in vitro by IL-4 during a 9- to 21-day culture. This stimulation was not observed in the absence of T cells. Inability of IL-4 to induce IgE in nonresponding cultures was associated with a failure to express CD23 on Lev-19+ natural killer cells; CD23 expression on B cells and monocytes was equivalent in responding and nonresponding subjects. Concentrated supernatants from Epstein-Barr virus-transformed B cell lines containing soluble fragments (sCD23) of the low-affinity Fc epsilon R (Fc epsilon R-II, CD23) induced IgE from all donors' cells in the absence of T cells. The sCD23 containing supernatants were demonstrated to be devoid of IL-4, and their effect could not be abrogated by anti-IL-4. IgE induction by both IL-4 and sCD23-containing supernatant were blocked by anti-CD23 monoclonal antibody. Affinity absorption of sCD23 removed the IgE-inducing activity. The cells most responsive to the sCD23 material were small, resting B cells rather than large in vivo activated cells. IL-4 synergized with sCD23-containing supernatant in the T cell-depleted cultures, and limiting dilution analyses demonstrated that IL-4 caused a more than tenfold increase in the precursor frequency of cells capable of responding to sCD23-containing supernatant with IgE production. These data are consistent with the hypothesis that IL-4 has multiple effects in the ultimate induction of human IgE including (1) commitment of B cells to IgE and (2) the generation of natural killer cell sCD23 fragments that subsequently drive IgE-committed cells to IgE synthesis.

Human IgG anti-F(ab')2 antibodies possess rheumatoid factor activity

Individual preparations of affinity purified anti-F(ab')2 antibodies and anti-Fc antibodies isolated from the sera of patients with rheumatoid arthritis (RA), were examined for reactivity with the Fab and Fc fragments of human IgG. Western blot assays demonstrated specific interaction of affinity-purified anti-Fab antibodies with both Fab and Fc molecules. Approximately one-half of the anti-Fab antibody preparations studied contained IgG antibodies reactive with Fab and Fc fragments in ELISA, suggesting the existence of naturally occurring epibody-like autoantibodies in these patients. Thirteen of 14 affinity-purified anti-Fc antibody preparations contained IgG cross-reactive with Fab molecules in ELISA. Double-adsorption assays on affinity columns demonstrated that a minimum of 14%, and possibly as much as 50%, of the IgG anti-Fab antibodies reacted with the Fc of IgG. Conversely, a minimum of 12%, and possibly as much as 70%, of the IgG anti-Fc antibodies reacted with IgG Fab molecules. Anti-Fab antibodies isolated from non-RA individuals also exhibited anti-Fc reactivity in ELISA, demonstrating the presence of these dual-reactive antibodies in other autoimmune and normal individuals. These studies establish the presence of naturally occurring IgG autoantibodies reactive with both the Fab and Fc fragments of human IgG. Their existence emphasizes the potential of anti-immunoglobulin antibodies to recognize a multiplicity of antigens, possibly including other members of the immunoglobulin supergene family.

Structural proteins of the Actinobacillus actinomycetemcomitans bacteriophage phi Aa

øAa is an A1 morphotype bacteriophage which infects certain strains of Actinobacillus actinomycetemcomitans. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of dissociated, purified phi Aa particles revealed 7 major structural proteins (P1-P7) ranging in size from 17.5 to 52.7 kilodaltons (Kd). Treatment of the intact phage particles with 67% dimethyl sulfoxide (DMSO) resulted in the separation of the virion head and tail subunits. Purification of the head subunits was accomplished by sucrose density gradient centrifugation of the DMSO-treated phage particles. The purified head subunits were composed of a single protein having an electrophoretic mobility which corresponded to a 39.5 Kd protein (P3) of the intact virus. Raising the pH of a purified phi Aa suspension to 12.7 disrupted the head subunits, as well as the tail tube and tail fibers, releasing intact contractile tail sheaths. The tail sheaths were collected by centrifugation. The purified tail sheaths were analyzed by SDS-PAGE and were found to be composed of two proteins (P1 and P2) having molecular weights of 52.7 and 41.2 Kd respectively. The location of each of the 4 remaining major structural proteins in the phi Aa virion remains to be determined.

AIDS Kaposi sarcoma-derived cells produce and respond to interleukin 6

Cell lines derived from Kaposi sarcoma lesions of patients with AIDS (AIDS-KS cells) produce several cytokines, including an endothelial cell growth factor, interleukin 1 beta, and basic fibroblast growth factor. Since exposure to human immunodeficiency virus increases interleukin 6 (IL-6) production in monocytes and endothelial cells produce IL-6, we examined IL-6 expression and response in AIDS-KS cell lines and IL-6 expression in AIDS Kaposi sarcoma tissue. The AIDS-KS cell lines (N521J and EKS3) secreted large amounts of immunoreactive and biologically active IL-6. We found both IL-6 and IL-6 receptor (IL-6-R) RNA by slot blot hybridization analysis of AIDS-KS cells. The IL-6-R was functional, as [3H]thymidine incorporation by AIDS-KS cells increased significantly after exposure to human recombinant IL-6 (hrIL-6) at greater than 10 units/ml. When AIDS-KS cells (EKS3) were exposed to IL-6 antisense oligonucleotide, cellular proliferation decreased by nearly two-thirds, with a corresponding decrease in the production of IL-6. The decrease from IL-6 antisense in AIDS-KS cell proliferation was reversed by the addition of hrIL-6. We confirmed that AIDS-KS cells produced IL-6 in vivo by preparing RNA and tissue sections from involved and uninvolved skin from a patient with AIDS Kaposi sarcoma. We detected immunoreactive IL-6 in the involved tumor areas and to a lesser extent in the surrounding normal epidermis. Slot blot hybridization showed a great excess of IL-6 and IL-6-R RNA in involved skin compared to uninvolved skin. These results show that both IL-6 and IL-6-R are produced by AIDS-KS cells and that IL-6 is required for optimal AIDS-KS cell proliferation, and they suggest that IL-6 is an autocrine growth factor for AIDS-KS cells.

Animal model of conjunctival primary acquired melanosis

A condition clinically identical to human conjunctival primary acquired melanosis (PAM) was induced in 16 of 20 Dutch (pigmented) rabbits after weekly topical 60-microliters applications of a 1% solution of 7,12-dimethylbenz[a]anthracene (DMBA) in acetone. Pigment stippling appeared in the conjunctiva as early as 5 weeks after the initial carcinogen application. Confluent patches of flat pigmentation appeared over the palpebral conjunctiva 18 weeks after the onset of treatment and showed progressive lateral enlargement and darkening. Histologically, a spectrum of changes from increased melanin production and melanocytic hyperplasia without atypia (resembling the human condition of PAM without atypia) through atypical melanocytic hyperplasia (resembling human PAM with atypia) was identified. The development of this model permits further investigations to explore and explain the clinically observed phenomenon of waxing and waning of PAM and its promotion to conjunctival malignant melanoma.

Serum IgG4 anti-Fab antibodies in rheumatoid arthritis are constitutively expressed

IgG4 comprises a significant proportion of the total anti-Fab antibody (aFABA) response in many but not all patients with rheumatoid arthritis (RA). Analyses of the dynamics of IgG aFABA subclass expression in 11 RA patients for periods of up to 11 months demonstrated that IgG4 aFABA was restricted to 6 of the 11 RA patients' sera initially studied and comprised approximately 25% (or more) of the total IgG aFABA response. Quantities of IgG4 aFABA in subsequent, serially obtained serum samples from these patients remained stable throughout the study period, whereas the remaining RA patients whose initial sera possessed small quantities of serum IgG4 aFABA failed to generate any augmented IgG4 aFABA response during the study. Elevated expression of IgG4 aFABA did not appear to be a consequence of a generalized polyclonal gammopathy or a generalized increase in autoantibody expression, though patients with higher total IgG4 serum levels expressed significantly greater quantities of IgG4 aFABA. These results indicate that the differential expression of IgG4 aFABA among RA patients reflects constitutive production within a subset of RA patients in whom IgG4 appears to comprise a significant proportion of the total IgG aFABA response.

The comparative cytotoxicity of periodontal bacteria

The direct cytotoxicity of sonic extracts (SE) from nine periodontal bacteria for human gingival fibroblasts (HGF) was compared. Equivalent dosages (in terms of protein concentration) of SE were used to challenge HGF cultures. The cytotoxic potential of each SE was assessed by its ability to (1) inhibit HGF proliferation, as measured by direct cell counts; (2) inhibit 3H-thymidine incorporation in HGF cultures; or (3) cause morphological alterations of the cells in challenged cultures. The highest concentration (500 micrograms SE protein/ml) of any of the SEs used to challenge the cells was found to be markedly inhibitory to the HGFs by all three of the criteria of cytotoxicity. At the lowest dosage tested (50 micrograms SE protein/ml); only SE from Actinobacillus actinomycetemcomitans, Bacteroides gingivalis, and Fusobacterium nucleatum caused a significant effect (greater than 90% inhibition or overt morphological abnormalities) in the HGFs as determined by any of the criteria employed. SE from Capnocytophaga sputigena, Eikenella corrodens, or Wolinella recta also inhibited cell proliferation and thymidine incorporation at this dosage; however, the degree of inhibition (5-50%) was consistently, clearly less than that of the first group of three organisms named above. The SE of the three other organisms tested (Actinomyces odontolyticus, Bacteroides intermedius, and Streptococcus sanguis) had little or no effect (0-10% inhibition) at this concentration. The data suggest that the outcome of the interaction between bacterial components and normal resident cells of the periodontium is, at least in part, a function of the bacterial species.

Recognition by anti-Fab antibodies in rheumatoid arthritis of structure(s) widely distributed on human Fab molecules

Anti-Fab antibodies (aFABA) of restricted clonality and acidic spectrotypes were isolated from the sera of patients with rheumatoid arthritis (RA). These aFABA reacted with multiple populations of pooled human Fab molecules, which had been charge separated by chromatofocusing techniques (CF), indicating that the structures recognized by these aFABA were present on a polyclonal population of Fab molecules. The structures were also widely distributed among the Fab repertoires of normal individuals, as well as individual autologous and heterologous RA patients. Thus, the aFABA did not appear to recognize highly restricted epitope(s), i.e. a private idiotope, limited in its expression to RA individuals. The determinants of the Fab molecules recognized by affinity purified aFABA could be defined by linear and/or conformational structures, depending upon the individual from which the aFABA were isolated. Additionally, some of the affinity purified aFABA also reacted with Fc fragments, suggesting the presence of epibody-like autoantibodies in this population. Lastly, size analysis of the circulating IgG4 aFABA complexes indicated that these autoantibodies were not complexed with intact IgG, but rather with a molecule of 40-60 kDa, further suggesting the potential for these autoantibodies to react with multiple antigens.

Defective memory B cell formation in patients with inflammatory bowel disease following tetanus toxoid booster immunization

Inflammatory bowel disease patients with mild to inactive disease were studied for their ability to generate pokeweed mitogen responsive anti-tetanus toxoid IgG producing B cells in the peripheral blood 21 days following in vivo tetanus toxoid booster immunization. Compared to normals and disease controls, patients with inflammatory bowel disease had significantly impaired in vitro production of anti-tetanus toxoid antibody during an 8 day pokeweed mitogen stimulated culture period. There was poor correlation between the ratio of helper to suppressor T cells in the peripheral blood and pokeweed mitogen stimulated antibody production. Likewise, there was little correlation between in vitro antibody production and peripheral blood natural killer cell cytotoxic activity. Culture of the patients B cells with normal T cells failed to improve antibody production in vitro. These results indicate that many inflammatory bowel disease patients have an impaired humoral immune response to tetanus toxoid booster immunization. This impaired immune response may be due to an inability to generate B cell precursors of anti-tetanus toxoid IgG producing B cells rather than to abnormal circulating helper or suppressor T cell activity or natural killer cell regulatory activity.

Purification and biochemical properties of a bacteriocin from Actinobacillus actinomycetemcomitans

Extracts of certain strains of Actinobacillus actinomycetemcomitans are inhibitory to strains of Streptococcus sanguis such as S. sanguis ATCC 10556. The isolation of a protein from an A. actinomycetemcomitans sonic extract which copurified with the inhibitory activity was accomplished by preparative isoelectric focusing, Sephadex G-100 gel filtration chromatography, and preparative polyacrylamide gel electrophoresis (PAGE). The resulting isolated protein, which focused at a pH of 6.1 to 6.3, appeared as a single band in anionic nondissociating PAGE analysis. This protein could be dissociated into two subunits with molecular weights of 50,000 and 70,000, which were resolvable by PAGE analysis. A 1,758-fold increase in specific activity was seen in the purified inhibitory protein compared with the crude sonic extract starting material. The properties of the inhibitory activity in the A. actinomycetemcomitans extract are characteristic of a bacteriocin. Accordingly, we propose the name actinobacillicin for the inhibitory protein.