Validity of parent report measures of vocabulary development for children with Down syndrome

This study investigated the validity of a parent report measure of vocabulary development, the MacArthur Communicative Development Inventory: Words and Sentences (CDI), in children with and without developmental disabilities. Concurrent validity was examined by comparing results from the CDI and laboratory measures of vocabulary in 44 children with Down syndrome and 46 typically developing children with mental ages from 12 to 27 months. Significant correlations between .70 and .82 were obtained. Predictive validity was examined by measuring the vocabulary of 20 children with Down syndrome and 23 typically developing children first at approximately 20 months mental age and later at a mental age of approximately 28 months. Significant correlations were obtained between the CDI at Time A and all but one of the vocabulary measures at Time B (r = .46 to .66). These results establish the validity of parent measures of vocabulary development for children with Down syndrome and confirm their validity for typically developing children.

Autoimmunity caused by ignorant CD8+ T cells is transient and depends on avidity

RIP-Kb mice, which express H-2Kb (Kb) molecules on their pancreatic beta cells, were used to examine the requirements for induction of autoimmune diabetes caused by CD8+ T cells. Previous studies showed that when these mice were crossed to mice expressing a Kb-specific TCR transgene, those CD8+ cells expressing the highest density of the transgenic TCR (presumably the highest avidity cells) were deleted intrathymically due to aberrant expression of Kb at this site. The remaining low avidity cells ignored Kb-bearing beta cells, even after priming, but were able to cause autoimmune diabetes when supplied with Il-2. To examine the properties of high avidity autoreactive CD8+ T cells, the thymic compartment of RIP-Kb mice was replaced with normal tissue to enable the maturation of CD8+ cells expressing the highest density of the transgenic TCR. These high avidity cells generally ignored Kb-expressing beta cells, but became autoaggressive after priming. Importantly, analysis of islet infiltration by CD8+ T cells revealed the presence of infiltrating cells in all mice examined within 3 wk of priming, but such infiltration was not usually apparent at later time points. In some cases, multiple primings were necessary for full development of autoimmunity. This implied that beta cells could act as transient targets for CD8+ T cell attack but could not sustain the stimulation of primed CD8+ cells. These studies indicate that the duration of priming stimulus and the avidity of the autoreactive CD8+ cells profoundly influence the severity of autoimmune disease.

Autoimmunity caused by ignorant CD8+ T cells is transient and depends on avidity

RIP-Kb mice, which express H-2Kb (Kb) molecules on their pancreatic beta cells, were used to examine the requirements for induction of autoimmune diabetes caused by CD8+ T cells. Previous studies showed that when these mice were crossed to mice expressing a Kb-specific TCR transgene, those CD8+ cells expressing the highest density of the transgenic TCR (presumably the highest avidity cells) were deleted intrathymically due to aberrant expression of Kb at this site. The remaining low avidity cells ignored Kb-bearing beta cells, even after priming, but were able to cause autoimmune diabetes when supplied with Il-2. To examine the properties of high avidity autoreactive CD8+ T cells, the thymic compartment of RIP-Kb mice was replaced with normal tissue to enable the maturation of CD8+ cells expressing the highest density of the transgenic TCR. These high avidity cells generally ignored Kb-expressing beta cells, but became autoaggressive after priming. Importantly, analysis of islet infiltration by CD8+ T cells revealed the presence of infiltrating cells in all mice examined within 3 wk of priming, but such infiltration was not usually apparent at later time points. In some cases, multiple primings were necessary for full development of autoimmunity. This implied that beta cells could act as transient targets for CD8+ T cell attack but could not sustain the stimulation of primed CD8+ cells. These studies indicate that the duration of priming stimulus and the avidity of the autoreactive CD8+ cells profoundly influence the severity of autoimmune disease.

Peripheral deletion of autoreactive CD8+ T cells in transgenic mice expressing H-2Kb in the liver

The response of T cells specific for liver antigens was examined in transgenic mice expressing the allogeneic major histocompatibility complex class I molecule H-2Kb (Kb) under the control of the sheep metallothionein promoter (Met-Kb mice). To follow the fate of Kb-specific T cells, and to prevent any aberrant thymic expression of the Kb transgene, the mice were thymectomized, lethally irradiated, protected with bone marrow cells from transgenic mice expressing in their T cells a Kb-specific T cell receptor identifiable by a clonotypic antibody, and given syngeneic non-transgenic thymus grafts. Although Kb-specific CD8+ T cells were produced in the thymus grafts of these manipulated Met-Kb mice, only small numbers of such cells could be detected in the spleen and lymph nodes. The livers, however, showed signs of damage and were heavily infiltrated by actively dividing CD8+ T cells. We provide strong evidence that the hepatocytes, not generally regarded as antigen-presenting cells, activated the Kb-specific CD8+ T cells and that these disappeared after a vigorous autoimmune response that resulted in deletion.

5-HT1B/1D agonist CGS-12066B attenuates clasp knife reflex in the cat

1. The effect of intrathecal injection of the selective serotonin (5-HT)1B/1D receptor agonist CGS-12066B maleate (825 nmol) was assessed on stretch-evoked clasp knife inhibition of hindlimb ankle extensor muscle reflex force in precollicular decerebrate cats in which neural transmission in dorsolateral spinal pathways was blocked bilaterally by focal cooling. 2. During cold block, ramp and hold stretches of the medial gastrocnemius muscle (MG) evoked only a brief reflex excitation that was followed by powerful, long-lasting inhibition (the clasp knife reflex). Both the amplitudes of peak force evoked by the ramp and sustained force output during the last 500 ms of the hold phase of the stretch were depressed by > 50%. 3. Reflex force output during the hold portion of stretch was significantly improved on postdrug cold block trials, although peak force remained depressed. CGS-12066B did not significantly alter stretch-evoked force output in decerebrate cats when spinal cord neural transmission was unimpaired. 4. These data suggest that selective 5-HT1B/1D agonists may be of therapeutic usefulness in the treatment of reflex disorders arising from partial spinal cord injury.

Expression of two T cell receptor alpha chains on the surface of normal murine T cells

We have previously reported that a subset of T cells in T cell receptor (TCR)-transgenic mice may express two different alpha chains on their surface. The expression of two functional alpha chains has also been demonstrated for human peripheral blood T cells. In this report, we show that a proportion of normal murine lymph node T cells express two functional alpha chains on their surface. The extrapolated frequency of these cells present in the normal repertoire ranges from 7-21%, with an average of 15%. Our analysis of a small number of antigen-specific T cell clones suggests that the frequency of antigen-responsive cells expressing two surface alpha chains is relatively low. This raises the possibility that dual alpha chain T cells may have a selective disadvantage in responding to specific antigen.

Recombinant Listeria monocytogenes as a live vaccine vehicle for the induction of protective anti-viral cell-mediated immunity

Listeria monocytogenes (LM) is a Gram-positive bacterium that is able to enter host cells, escape from the endocytic vesicle, multiply within the cytoplasm, and spread directly from cell to cell without encountering the extracellular milieu. The ability of LM to gain access to the host cell cytosol allows proteins secreted by the bacterium to efficiently enter the pathway for major histocompatibility complex class I antigen processing and presentation. We have established a genetic system for expression and secretion of foreign antigens by recombinant strains, based on stable site-specific integration of expression cassettes into the LM genome. The ability of LM recombinants to induce protective immunity against a heterologous pathogen was demonstrated with lymphocytic choriomeningitis virus (LCMV). LM strains expressing the entire LCMV nucleoprotein or an H-2Ld-restricted nucleoprotein epitope (aa 118-126) were constructed. Immunization of mice with LM vaccine strains conferred protection against challenge with virulent strains of LCMV that otherwise establish chronic infection in naive adult mice. In vivo depletion of CD8+ T cells from vaccinated mice abrogated their ability to clear viral infection, showing that protective anti-viral immunity was due to CD8+ T cells.

Ectopic expression of the flagellar regulon alters development of the Bordetella-host interaction

Signal transduction molecules within the two-component family represent a conserved adaptation for the control of genes involved in pathogenesis. The Bordetella virulence control locus, bvgAS, activates and represses gene expression in response to environmental signals. While infection requires virulence gene activation, the role of gene repression during infection is not understood. By altering regulatory genes and reversing regulatory connections, we found evidence that the BvgAS-repressed genes responsible for motility are neither required nor expressed during colonization of the host. Expression of this Bvg- phase-specific phenotype in the Bvg+ growth phase resulted in a defect in tracheal colonization. Therefore, BvgAS promotes virulence both by activating genes required for colonization and by repressing genes that inhibit the development of infection.

Focal expression of interleukin-2 does not break unresponsiveness to "self" (viral) antigen expressed in beta cells but enhances development of autoimmune disease (diabetes) after initiation of an anti-self immune response

The participation of IL-2 in insulin-dependent (type 1) diabetes (IDDM) was analyzed in transgenic (tg) mice expressing the nucleoprotein (NP) of lymphocytic choriomeningitis virus and IL-2 under control of the rat insulin promoter focally in beta cells of the islets of Langerhans. Insertion and expression of the viral (self) gene or of the IL-2 gene alone did not lead to IDDM. Infiltration primarily of CD4 and B lymphocytes and increased expression of MHC class I and II molecules occurred in islets where IL-2 was expressed. By contrast, neither cellular infiltrates nor expression of MHC class I or II glycoproteins above base levels was noted in tgs expressing the viral protein alone. Double tg mice expressing both the viral protein and IL-2 in their islets displayed a modest increase in incidence of spontaneous diabetes compared with that of single transgenic mice expressing IL-2 alone. Breaking of immunological unresponsiveness or sensitization to self antigens did not occur. Neither cytotoxic T lymphocytes (CTL) nor antibodies directed against the viral tg (NP) were generated. However, after challenge with lymphocytic choriomeningitis virus, double tg mice developed anti-self (viral) CTL and IDDM (incidence > 95%) within 2 mo. The generation of virus ("self")-specific MHC-restricted CTL was dependent on CD4+ help. In contrast, viral inoculum to single tg mice expressing either the viral protein or IL-2 failed to enhance the incidence of IDDM over 30% for viral protein or 10% for IL-2 after an 8-mo observation period. Hence, in this autoimmune model in situ expression of IL-2 did not break unresponsiveness but markedly enhanced ongoing disease.

Autoantigen-induced deletion of peripheral self-reactive T cells

There are now numerous reports documenting the deletion of mature peripheral specific T cells following massive antigenic stimulation. Such a phenomenon can be regarded as a homeostatic mechanism to prevent unrestricted growth of antigen-activated clones and to safeguard against autoimmunity. Some of the reports examining this issue are summarized in this review and the role of the liver in tolerance and autoimmunity is discussed based on recent work performed with transgenic mice.

T-cell tolerance and autoimmunity in transgenic models of central and peripheral tolerance

Experiments with transgenic mice expressing genes encoding both antigens in defined tissues and T-cell receptor genes of known specificities have enhanced our understanding of the mechanisms involved in the pathogenesis of autoimmune states. They have also shed light on the means by which potentially autoreactive cells may be prevented from exerting their autoaggressive potential. The value of the transgenic approach is that it can overcome the low frequency of peptide-specific T cells occurring in normal animals, and also provide a tissue-specific, cognate antigen that is absent in controls. These factors allow reactive T cells to be isolated or quantified by flow cytometry and their responses to antigen in vitro and in vivo be defined.

Genetic requirements for acceleration of diabetes in non-obese diabetic mice expressing interleukin-2 in islet beta-cells

Diabetes was dramatically accelerated in non-obese diabetic (NOD) transgenic mice that expressed interleukin-2 (IL-2) in their beta cells. A single cross to C57BL/6 completely prevented this effect and a further backcross to the NOD genetic background showed that at least two diabetes susceptibility loci (Idd1s and Idd3/10s) were required for the diabetes acceleration T cells activated to islet antigens were not circulating in the mice. The accelerating effect of IL-2 was present; but decreased, in NOD mice that lacked CD8+ T cells as well as in NOD SCID mice. The implications are that in the NOD genetic background, the production of cytokines, such as IL-2, by islet-specific CD4+ T cells can lead to beta cell damage and diabetes and that CD8+ T cells may have a role in accelerating diabetes onset.

A prospective longitudinal study of language development in late talkers

This longitudinal investigation charted the course of cognitive and language development from the prelinguistic period to multiword productions in 19 typically developing (TD) toddlers and 4 toddlers who were subsequently identified as having late onset of expressive language. Assessments were conducted at 3-month intervals over a 21-month period, with 12 months of prospective assessment data comparing the TD and late talker (LT) subjects (mean CA: 13 to 25 months) and 9 months of follow-up data (mean CA: 25-34 months) on the 4 subjects who were identified as late talkers at age 2. Three different developmental profiles were identified, and predictors of expressive language outcomes for the LT subjects were evaluated.

BvgAS-mediated signal transduction: analysis of phase-locked regulatory mutants of Bordetella bronchiseptica in a rabbit model

Members of the Bordetella genus alternate between two distinct phenotypic phases in response to changes in their environment. This switch, termed phenotypic modulation, is mediated by the BvgAS sensory transduction system. We developed an animal model based on the interaction of Bordetella bronchiseptica with one of its natural hosts, the rabbit. To investigate the importance of BvgAS signal transduction, we constructed constitutive (RB53) and Bvg- (RB54) phase-locked derivatives of a wild-type strain, RB50. RB50 and RB53, but not RB54, established respiratory infections in B. bronchiseptica-free rabbits with an intranasal 50% infective dose of less than 200 organisms, and the course of the infection closely resembled that observed with naturally infected rabbits. Bacteria were recovered from the nasal cavity, larynx, trachea, and lungs in similar numbers from RB50- and RB53-infected rabbits, yet no pathology was detected by histological examination of lung and tracheal sections. The antibody responses in rabbits inoculated with RB50 or RB53 were quantitatively and qualitatively indistinguishable; high titers of antibodies were generated primarily against Bvg(+)-phase-specific antigens. No response against flagella, a Bvg- phase factor, was detected. Assessment of bacteria associated with alveolar macrophages indicated that only a small percentage of bacteria, if any, appear to be residing within lung macrophages. We also tested the ability of these strains to survive in a nutrient poor environment, conditions which may be encountered within certain niches in the host or in an environmental reservoir. The Bvg- phase was advantageous for growth under these conditions. Our results indicate the Bvg+ phase is sufficient for establishment of respiratory tract infection in the rabbit and the normal BvgAS-mediated response to environmental signals is not required during initial colonization. The Bvg- phase may play a role at later stages of infection, including persistence, transmission, or survival in the environment.

The thymus: maestro of the immune system

The thymus has been an enigmatic organ for centuries. Its true function was revealed only in 1961 when it was shown to be responsible for the proper development of the immune system. This finding has revolutionized the science of immunology and has led to a better understanding of the mechanisms involved in resistance to infections and of the pathogenesis of autoimmune and immunodeficiency diseases.

Reduction in postsynaptic inhibition during maintained electrical stimulation of different nerves in the cat hindlimb

1. Steady-state postsynaptic potentials (PSPs) were generated by prolonged (approximately 1 s) high-frequency (100-200 Hz) electrical stimulation of nerves in the cat hindlimb. The characteristics of these steady-state PSPs were compared for two polysynaptic afferent pathways (ipsilateral cutaneous sural vs. contralateral peroneal nerves), two animal preparations (decerebrate vs. chloralose), and two motoneuron pools (medial gastrocnemius vs. lateral gastrocnemius-soleus). 2. PSPs from both nerves usually (36 of 51 cases) contained a mixture of depolarizing and hyperpolarizing components. In all 36 cases where the PSP contained a hyperpolarizing component, a consistent qualitative pattern emerged during prolonged stimulation: the hyperpolarization reached a peak approximately 20 ms after stimulation onset and then decayed with a biphasic time course that consisted of an initial rapid phase (20-40 ms) and a later slower phase (200-400 ms) before the steady-state value was reached. This pattern occurred regardless of the differences in polysynaptic afferent pathways, animal preparations, and motoneuron pools. 3. The consistency of this overall pattern was remarkable, given the existence of several quantitative differences among the PSPs. These differences include the following: hyperpolarizing components were least common in the sural and peroneal PSPs in the decerebrate preparation. And only these sural and peroneal PSPs tended to have prolonged afterpotentials after stimulus cessation. The steady-state sural PSPs in the decerebrate preparation tended to generate the largest PSPs and, moreover, these PSPs did not follow the overall trend of having a statistically significant relation between the amplitude of the initial hyperpolarization and the amount of its decay. Finally, transient sural PSPs in lateral gastrocnemius-soleus motoneurons in the decerebrate preparation tended to have the largest hyperpolarizations. 4. To determine whether the decay of the hyperpolarization and the subsequent dominance of depolarization was due to a decreased inhibition or an increased excitation, injected current pulses were utilized to measure the changes in the cell's input resistance during the course of the synaptic input. A strong decrease in input resistance accompanied the initial period of maximal hyperpolarization (50% with respect to the resting input resistance). Input resistance then returned toward resting values as hyperpolarization faded and depolarization became dominant. However, there remained a persistent decrease in input resistance during the final phase of the PSP that amounted to < 10% of the initial decrease. These findings indicated that much of the reduction in hyperpolarization reflected a progressive decrease in synaptic efficacy for the inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Consequences of in situ production of IL-2 for islet cell death

Transgenic mice that expressed a single-copy IL-2 transgene in their pancreatic beta cells were previously shown to develop a massive inflammation in and around the islets, but did not progress to diabetes. When these mice were made homozygous for the transgene, diabetes did ensue in most animals by 200 days. Analysis of the T cells present in the pancreatic infiltrates of single-copy and homozygous rat insulin promoter IL-2 mice showed a predominance of CD4+ cells which was especially apparent in the very young mice. Furthermore, many of the CD4+ T cells in young mice displayed a memory-like phenotype in that they expressed higher levels of adhesion molecules and the IL-2R p55 marker. When the IL-2 transgene was introduced into nude mice, an almost identical pathology of inflammation was seen except that the infiltrating cells were mostly B cells. Expression of the same transgene in scid mice also resulted in an inflammatory response and in some situations it was sufficient to induce diabetes. From these results it appears that the T cell product, IL-2, in the absence of antigen-specific T or B cells can induce an inflammatory response of sufficient intensity to cause diabetes.

Autophosphorylation and phosphotransfer in the Bordetella pertussis BvgAS signal transduction cascade

Expression of adhesins, toxins, and other virulence factors of Bordetella pertussis is under control of the BvgA and BvgS proteins, members of a bacterial two-component signal transduction family. BvgA bears sequence similarity to regulator components, whereas BvgS shows similarity to both sensor and regulator components. BvgA and the cytoplasmic portion of BvgS ('BvgS) were overexpressed and purified. 'BvgS autophosphorylated with the gamma-phosphate from [gamma-32P]ATP and phosphorylated BvgA. Kinetic analysis indicated that BvgA receives its phosphate from 'BvgS. Mutations in the transmitter, receiver, and C-terminal domains of BvgS were tested for activation of a BvgAS-dependent fhaB::lacZ reporter fusion in vivo and for autophosphorylation and phosphotransfer to BvgA in vitro. All mutations abolished activation of the fhaB::lacZ fusion. A point mutation in the transmitter (H729Q) prevented autophosphorylation of 'BvgS. In contrast to other characterized sensor proteins, autophosphorylation also required sequences in the 'BvgS receiver and C-terminal domains. A 'BvgS receiver point mutation (D1023N) had the novel phenotype of being able to autophosphorylate but unable to transfer the phosphate to BvgA. Autophosphorylation activity of the D1023N mutant protein was kinetically and chemically indistinguishable from wild-type 'BvgS despite an uncoupling of phosphotransfer from autophosphorylation. 'BvgS was shown to contain primarily amidyl phosphate and BvgA an acyl phosphate linkage. We present a model for a phosphorelay controlling virulence gene expression in B. pertussis.

Failure of a protective major histocompatibility complex class II molecule to delete autoreactive T cells in autoimmune diabetes

The association of major histocompatibility complex genes with autoimmune diseases is firmly established, but the mechanisms by which these genes confer resistance or susceptibility remain controversial. The controversy extends to the nonobese diabetic (NOD) mouse that develops disease similar to human insulin-dependent diabetes mellitus. The transgenic incorporation of certain class II major histocompatibility complex genes protects NOD mice from diabetes, and clonal deletion or functional silencing of autoreactive T cells has been proposed as the mechanism by which these molecules provide protection. We show that neither thymic deletion nor anergy of autoreactive T cells occurs in NOD mice transgenic for I-Ak. Autoreactive T cells are present, functional, and can transfer diabetes to appropriate NOD-recipient mice.

Expression of two alpha chains on the surface of T cells in T cell receptor transgenic mice

CD8+ T cells taken directly from mice expressing a Kb-specific T cell receptor (TCR) transgene expressed the transgenic TCR in a bimodal profile as detected by flow cytometric analysis using a clonotype-specific monoclonal antibody. Those cells expressing the lower density of the transgenic TCR expressed the transgenic beta chain and two different alpha chains on their surface. One alpha chain was the product of the alpha transgene, whereas the other was derived by endogenous rearrangement. This report provides the first demonstration that T cells isolated directly from mice may express two different TCR clonotypes on their surface. The potential consequences of this finding for studies using TCR transgenic mice and for the induction of autoimmunity are discussed.

Conversations with children who are language impaired: asking questions

Samples of conversational language were elicited with a standardized interview protocol from 24 children, aged 2:6 to 7:8, half with specific language impairment (SLI), half with normally developing language (LN), matched for language level. Samples were analyzed to determine whether there were associations between adult questioning and children's use of ellipsis. For the SLI children, but not the LN children, increased proportions of questions were significantly correlated to increased proportions of ellipsis. This finding has implications for the use of MLU measures in clinical and research practice.

Comparison of two methods for promoting productive vocabulary in late talkers

This investigation compared the effectiveness of two language treatment methods, modeling versus modeling plus evoked production, in promoting productive vocabulary in three toddlers identified as late talkers. A single-subject alternating treatments design was employed in this study in which different sets of words were taught under the two treatment methods during group and individual instruction. Some evidence of differential patterns of response to the treatment types was found for two subjects, but the subjects differed as to which particular treatment method was associated with better performance. Neither treatment method was effective for the third subject. Dynamic assessment measures were only marginally useful in predicting overall lexical learning potential in these subjects, and did not predict response to the two teaching methods. Implications of these results are discussed with regard to the role of language intervention for late talkers.