Lysosomal protein thermal stability does not correlate with cellular half-life: global observations and a case study of tripeptidyl-peptidase 1

Late-infantile neuronal ceroid lipofuscinosis (LINCL) is a neurodegenerative lysosomal storage disorder caused by mutations in the gene encoding the protease tripeptidyl-peptidase 1 (TPP1). Progression of LINCL can be slowed or halted by enzyme replacement therapy, where recombinant human TPP1 is administered to patients. In this study, we utilized protein engineering techniques to increase the stability of recombinant TPP1 with the rationale that this may lengthen its lysosomal half-life, potentially increasing the potency of the therapeutic protein. Utilizing multiple structure-based methods that have been shown to increase the stability of other proteins, we have generated and evaluated over 70 TPP1 variants. The most effective mutation, R465G, increased the melting temperature of TPP1 from 55.6°C to 64.4°C and increased its enzymatic half-life at 60°C from 5.4 min to 21.9 min. However, the intracellular half-life of R465G and all other variants tested in cultured LINCL patient-derived lymphoblasts was similar to that of WT TPP1. These results provide structure/function insights into TPP1 and indicate that improving in vitro thermal stability alone is insufficient to generate TPP1 variants with improved physiological stability. This conclusion is supported by a proteome-wide analysis that indicates that lysosomal proteins have higher melting temperatures but also higher turnover rates than proteins of other organelles. These results have implications for similar efforts where protein engineering approaches, which are frequently evaluated in vitro, may be considered for improving the physiological properties of proteins, particularly those that function in the lysosomal environment.

Ultrastructural characterization of epithelial cell membranes in normal human conducting airway epithelium: A freeze-fracture study

Cell membranes of normal human nasal and tracheal epithelium were characterized by means of freeze-fracture preparations. These investigations illustrated a predictable variability in the distribution of membrane-associated particles on PF-faces of different cell types and in different regions of the same cell. Details of the fine structure and variability of tight junctional complexes in different cell types are presented as are ultrastructural perspectives of cell membrane involvement in ciliogenesis and in mucus secretion. Because ciliogenic profiles and nascent tight junctional complexes were observed more frequently in nasal epithelial cells, these features provided markers of cellular differentiation. Based on the frequent appearance of such indicators, these observations suggested that cell turnover may be more rapid in the region of the nasal turbinates than in the trachea. There was no appreciable evidence of ultrastructural variability between the epithelial cell membranes of similar cell types in the upper and lower respiratory tract.

Initiation of RNA Polymerization and Polymerase Encapsidation by a Small dsRNA Virus

During the replication cycle of double-stranded (ds) RNA viruses, the viral RNA-dependent RNA polymerase (RdRP) replicates and transcribes the viral genome from within the viral capsid. How the RdRP molecules are packaged within the virion and how they function within the confines of an intact capsid are intriguing questions with answers that most likely vary across the different dsRNA virus families. In this study, we have determined a 2.4 Å resolution structure of an RdRP from the human picobirnavirus (hPBV). In addition to the conserved polymerase fold, the hPBV RdRP possesses a highly flexible 24 amino acid loop structure located near the C-terminus of the protein that is inserted into its active site. In vitro RNA polymerization assays and site-directed mutagenesis showed that: (1) the hPBV RdRP is fully active using both ssRNA and dsRNA templates; (2) the insertion loop likely functions as an assembly platform for the priming nucleotide to allow de novo initiation; (3) RNA transcription by the hPBV RdRP proceeds in a semi-conservative manner; and (4) the preference of virus-specific RNA during transcription is dictated by the lower melting temperature associated with the terminal sequences. Co-expression of the hPBV RdRP and the capsid protein (CP) indicated that, under the conditions used, the RdRP could not be incorporated into the recombinant capsids in the absence of the viral genome. Additionally, the hPBV RdRP exhibited higher affinity towards the conserved 5'-terminal sequence of the viral RNA, suggesting that the RdRP molecules may be encapsidated through their specific binding to the viral RNAs during assembly.

A comparison of the functional difficulties in staged and simultaneous open carpal tunnel decompression

There is no agreement about whether patients with bilateral carpal tunnel syndrome should undergo staged or simultaneous open decompression. The purpose of this study was to quantify and compare the functional difficulties during the recovery from surgery for patients undergoing staged or simultaneous decompressions. Sixty-three patients had surgery; 33 had staged decompression (Group 1) and 30 simultaneous decompressions (Group 2). Functional difficulties were recorded using the Levine and Quick-DASH scores along with a visual analogue score for pain. There were no complications in either group. There was no significant difference in terms of pain or satisfaction. Functional difficulties were greater in the simultaneous group; however, there was no difference in completing simple tasks. Patients reported high satisfaction with either management approach. However, significantly fewer would consider undergoing simultaneous decompression again.

Diphtheria pathogenesis in Guinea pig tracheal organ culture

The effect of diphtheria toxin on guinea pig trachea in organ culture was examined to measure the susceptibility of respiratory epithelial cells to toxin action. Exposure of individual tracheal rings to toxin resulted in cessation of protein synthesis as well as the development of cytopathology within a few hours. Continued incubation led to further inhibition of protein synthesis and extensive disorganization of the epithelial layer. Other inhibitors of protein synthesis were monitored for their effect on the structural integrity of tracheal cells but were found incapable of eliciting similar histopathology. Early after its addition, toxin at minute concentrations possessed cytotoxic properties as well as the ability to inhibit protein synthesis. Interpretation of these data is correlated with current information on the structure and activity of diphtheria toxin.

Characterization of an axonemal dynein heavy chain expressed early in airway epithelial ciliogenesis

The most conspicuous evidence of airway epithelial maturation and vitality is the presence of motile cilia. In an effort to generate genetic and antigenic markers of airway maturation, injury, and repair, we characterized airway epithelial expression of a gene identified by two human expressed sequence tags that encoded peptides with sequence similarity to an invertebrate ciliary dynein heavy chain (DHC). Molecular analyses showed that the gene has a very large RNA transcript that encodes a very high molecular weight polypeptide with biochemical properties that are characteristic of a dynein heavy chain. Expression of the gene transcript correlated with the presence of ciliated cells in tissues, and immunohistochemical localization of the gene product confirmed its presence in the cilia of mature airway epithelium. In epithelium undergoing ciliogenesis ex vivo, expression of the gene transcript preceded ciliation of the epithelium and the gene product was present in the cytoplasm and at the apical border of nonciliated cells. These data suggested that the gene encodes an axonemal DHC that is expressed early during ciliogenesis, before the appearance of cilia.

Computer-assisted analysis of radial symmetry in human airway epithelial cilia: assessment of congenital ciliary defects in primary ciliary dyskinesia

The ultrastructural analysis of cilia and diagnosis of primary ciliary dyskinesia (PCD) in biopsies of airway epithelium is sometimes confounded by poor sampling, inconsistencies in tissue quality and processing, and other technical problems. Although clinical findings may lead to a presumptive diagnosis, ultrastructural analysis of ciliary axonemes is the standard for confirmation of PCD. The ultrastructural features of the cilium when viewed in cross section by transmission electron microscopy confer a radial symmetry to the axoneme. Current digital image processing techniques can be applied to such images to reinforce signal, diminish noise, and confirm consistency of position of axonemal structures, a process that can augment ultrastructural analysis for PCD. In this study, computer-assisted digital image processing was used to evaluate cross sections of cilia in airway epithelial biopsies from patients previously diagnosed with PCD as well as in control subjects with normal cilia. These studies supported the original diagnoses and provided some new insights into axonemal organization in PCD. This technique is simple and may be useful in providing a supporting means for confirming or ruling out a diagnosis of PCD in cases that appear equivocal.

An autoradiographic assessment of epithelial cell proliferation and post-natal maturation of the tracheal epithelium in infant ferrets

The tracheal epithelium of infant ferrets undergoes rapid postnatal maturation over the first month of life to achieve the pseudostratified columnar configuration characteristic of the large airways of other mammals. We have used in vivo pulsing with tritiated thymidine ((3)HT) to elicit autoradiographic labeling of cells synthesizing nucleic acids in order to characterize more fully the contribution to development of different cell types comprising the nascent epithelial layer during this period of rapid growth. These studies indicate that two distinct populations of epithelial cells possess proliferative potential and contribute to the establishment of the mature adult epithelial layer. These investigations further confirm the mitotic potential of basal cells during a period of rapid postnatal growth and development of the tracheal epithelial layer. These studies also document the contribution to early airway development by non-ciliated cells, which predominate on the luminal border of the ferret trachea at birth. The temporal and histologic patterns of airway epithelial maturation during post-natal life in the ferret as contained in this study exhibit similarities to those which occur with recovery from injury by infection and irritant exposure in mature airways. Thus, the characterization of epithelial cell compartments having proliferative potential may provide insights into the mechanisms whereby normal airway epithelial organization is established and maintained during development as well as the possible recapitulation of these mechanisms during times of epithelial regeneration following injury.

Connexin 26 expression in human and ferret airways and lung during development

Coordinated microscopic and molecular biological studies were used to document gap junction expression during postnatal development in ferret tracheal epithelium and lung and in fetal and adult human airway and lung. Expression of connexin 26 (Cx26) in the ferret airways was limited to the epithelial layer and was observed only during the newborn interval. In contrast, we found Cx26 expressed in the alveolar epithelium of the ferret lung by in situ hybridization, Northern blotting, RT-PCR amplification, and immunocytochemical labeling at all ages examined. This finding was further confirmed by documentation of gap junctional plaques upon ultrastructural examination of freeze-fracture replicas of adult ferret lung tissue. Parallel studies of developing human fetal lung and airway suggested connexin expression in the airways only in the first trimester but, as in the ferret, persistent expression was observed in both fetal and adult lung. These studies suggest that the transient expression of Cx26 is a reliable early indicator of airway epithelial development and differentiation in the airways. In contrast, Cx26 expression persists throughout life in the lung, suggesting that gap junctions serve more perennial intercellular communication functions in the peripheral lung.

Variability in distribution and populations of gap junctions in ferret trachea during postnatal development

Immunocytochemical probes have been used to characterize gap junction distribution in the postnatal ferret trachea by epifluorescence and by laser scanning confocal and electron microscopy. A battery of antibodies directed against fragments of different connexins localized beta 1- and beta 2-gap junction antigens (connexins 32 and 26, respectively) at the intercellular borders of the superficial epithelium while alpha 1-gap junction antigen (connexin 43) was localized to the loose connective tissues. Gap junction labeling in the superficial epithelium declined in the first weeks of life but persisted in the developing submucosal glands to the weanling stage. Localization of the alpha- and beta-antigens was specific for connective tissues and epithelial layers, respectively. These observations suggest that communication competence is an important component of early development in the mammalian airways.

Microtubular discontinuities as acquired ciliary defects in airway epithelium of patients with chronic respiratory diseases

A critical relationship exists between ordered ciliary ultrastructure and optimal mucociliary clearance in the respiratory airways. Structurally defective cilia derived from heritable syndromes or from epithelial cell injury may promote or exacerbate chronic disease processes. A lesion of airway epithelial cilia characterized by microtubular discontinuities and previously associated with primary ciliary dyskinesia (PCD) has been documented in other forms of chronic airways diseases, including cystic fibrosis (CF). Nasal cilia obtained by curettage of the inferior nasal turbinate from 89 patients without CF but exhibiting symptoms favoring PCD were evaluated by transmission electron microscopy. Of the 89 patients in the study group, 19 (21.4%) were diagnosed with PCD. Among the PCD patients, 16 (84.2%) exhibited microtubular discontinuities. Nine patients from this group without ultrastructural evidence of PCD also exhibited these defects, however. Furthermore, seven of eight nasal biopsy specimens from patients with CF in a separate disease control group exhibited microtubular discontinuities. Microtubular discontinuities were quantitatively negligible among control groups of healthy human subjects and individuals experimentally and naturally subjected to acute airway injury. These data provide evidence that ciliary microtubular discontinuities represent acquired ciliary defects reflective of chronic airway disease injury and are not components of a primary structural abnormality in PCD.

Effect of nitrogen dioxide on human nasal epithelium

The nasal epithelium of young adult white men in good health was evaluated by electron microscopy in a condition blind fashion relative to exposures of 2 ppm nitrogen dioxide (NO2) or clean air for 4 h. The exposure protocol involved two separate exposures of the same individuals to NO2 or clean air approximately 3 wk apart. We found qualitative and quantitative evidence that luminal border membranes of ciliated cells were ultrastructurally altered in six of seven samples of nasal epithelium obtained following NO2 exposures, although subsequent morphometric statistical analyses were not significant. This alteration was characterized by cilia containing excess matrix in which individual or, more commonly, multiple ciliary axonemes were embedded, and by vesiculations of luminal border ciliary membranes, a pattern less common in clean air-exposed control specimens. Although these patterns were not widespread, their morphology was consistent with findings of previous animal studies involving acute and chronic exposure to NO2. Our findings suggest that adverse effects on mucociliary function in normal humans due to acute exposure to low levels of NO2 are most likely minimal. However, in view of other reports of NO2 exposure in laboratory animals documenting ciliary injury, our observations support a view that similar patterns might appear more prominently with higher NO2 levels and/or more extended exposure intervals.

Nitrogen dioxide exposure and urinary excretion of hydroxyproline and desmosine

The relationship between average and peak personal exposure to nitrogen dioxide and urinary excretion of hydroxyproline and desmosine was investigated in a population of preschool children and their mothers. Weekly average personal nitrogen dioxide exposures for subjects who resided in homes with one or more potential nitrogen dioxide source (e.g., a kerosene space heater, gas stove, or tobacco smoke) ranged between 16.3 and 50.6 ppb (30.6 and 95.1 micrograms/m3) for children and between 16.9 and 44.1 ppb (12.8 and 82.9 micrograms/m3) for mothers. In these individuals, the hydroxyproline-to-creatinine and desmosine-to-creatinine ratios were unrelated to personal nitrogen dioxide exposure--even though continuous monitoring documented home nitrogen dioxide concentration peaks of 100-475 ppb lasting up to 100 h in duration. Significantly higher hydroxyproline-to-creatinine and desmosine-to-creatinine ratios were observed in children, compared with mothers (p < .001 and .003, respectively).

Ultrastructure of airway epithelial cell membranes among patients with cystic fibrosis

Alterations in transepithelial ion fluxes are a primary pathophysiologic feature in cystic fibrosis (CF). Chronic respiratory infections and host responses are secondary aggravating pulmonary complications of this disease. In the present study, the application of the freeze-fracture technique to samples of nasal and tracheal epithelium from patients with CF has provided a perspective of large areas of cell membrane for the evaluation of possible structural correlates to the pathophysiology of this disease. A variety of aberrant configurations in stranding pattern and disorganization of the epithelial tight junctional complexes in CF airway epithelium are described. Additionally, examination of ciliary membranes revealed the presence of compound cilia and dysmorphology of ciliary necklace configuration. These features are thought to represent acquired structural lesions possibly derived from chronic infection and/or host responses which may further exacerbate abnormal ion transport properties and decrements of ciliary function that appear to be associated with the airway epithelium of individuals with CF.

Dynamics of intercellular communication and differentiation in a rapidly developing mammalian airway epithelium

A considerable body of data suggests that gap junctions represent channels that facilitate intercellular communication, thereby modulating growth and development. However, direct quantitative evidence supporting such a structure/function relationship is limited. This study has identified a new model in the rapidly developing tracheal epithelium of infant ferrets wherein gap junction prevalence and intercellular transfer of a fluorescent, low molecular weight dye, epithelial cell incorporation of tritiated thymidine, and progressive ciliation of the epithelium have been characterized. This developmental pattern provides favorable conditions for the study of relationships between gap junctions, intercellular translocation of chemical signals, and cell growth and differentiation in a mammalian airway epithelium with a minimum of experimental intervention.

Nucleotide sequence of the MgPa (mgp) operon of Mycoplasma genitalium and comparison to the P1 (mpp) operon of Mycoplasma pneumoniae

The attachment of Mycoplasma genitalium and Mycoplasma pneumoniae to ciliated epithelium involves two surface proteins designated MgPa and P1, respectively. We have previously cloned and sequenced the P1 (mpp) operon of M. pneumoniae, and report here the use of P1-derived probes to clone and sequence a 10.4-kb region of M. genitalium DNA that, by analogy to the P1 operon, contains the MgPa (mgp) operon. The deduced amino acid sequences of the 29-kDa (ORF-1), MgPa (160-kDa) and 114-kDa (ORF-3) proteins of the MgPa operon show extensive homologies with those of the 28-kDa, P1 (170-kDa) and 130-kDa proteins, respectively, encoded by the P1 operon. The common features and homology of these operons are consistent with previous observations that the MgPa and P1 proteins share cross-reactive epitopes, as well as similar biological function. The gene order of the MgPa operon is ORF-1, MgPa, ORF-3, with intervening regions of 6 and 1 nt, respectively. A consensus ribosome-binding site (RBS) sequence is found before ORF-1 and a sequence indicative of a transcription terminator is located beyond ORF-3; the absence of such sequences adjacent to the MgPa gene suggests that the operon is transcribed as a polycistronic message. The RBS sequence is followed by sequences of dyad symmetry that have the potential to form two alternative stem-and-loop structures, which could be involved in controlling initiation of translation.

Otitis media in early childhood and cognitive, academic, and classroom performance of the school-aged child

The relationship between the occurrence of otitis media during the first 3 years of life and cognitive, academic, and classroom performance during the third year of elementary school was evaluated in 44 socioeconomically disadvantaged children. The children attended a research day-care program where their otitis media experience and psychoeducational development were documented prospectively from birth. No significant relationship was found between otitis media in early childhood and performance on tests of verbal intelligence or academic achievement in the third year of school. The number of days of otitis media before 3 years of age was significantly correlated with teachers' ratings of children's attentional behavior in the classroom, however. Children with more early otitis media tended to be rated as less task oriented and less able to work independently than children with less otitis media. This was an exploratory study of a small number of children. Further study of the potential association is needed.

Development, organization, and function of tight junctional complexes in the tracheal epithelium of infant ferrets

The surface epithelium of newborn ferret airways matures rapidly in the first month of life. Prominent developmental features include a transition from predominantly non-ciliated to ciliated cells, quantitative and qualitative changes in secretion of macromolecules, and a transition from secretory to absorptive patterns of ion transport. Freeze-fracture replicas of ferret tracheal epithelium from 0 to 28 days of age exhibited progressive developmental patterns in tight junctional structure from beaded, unclosed patterns in newborns to more closed patterns at 28 days. Strand number increased while the depth of tight junctional structures and the proportion of strands exhibiting discontinuity decreased postnatally. Total transepithelial conductance, paracellular conductance, and cell size decreased over the first month. Our data suggest that changes in physiological parameters that reflect epithelial tight junction permeability can be attributed, at least in part, to maturation of this intercellular junction during the postnatal period.

Ciliary defects: cell biology and clinical perspectives

Considerable progress has been made in achieving a perspective of the pathophysiology of ciliary defects in human disease in the interval between Siewert's and Kartagener's early descriptions of KS. Not only have we achieved a better understanding of some of the mechanisms involved in the pathogenesis of congenital ciliary syndromes, but also we have come to appreciate a new spectrum of ciliary defects, those of acquired etiology. The advent of modern electron microscopy has been a significant element to this progress and its importance is reflected by the numerous studies of ciliary defects that have come in the wake of the pioneering ultrastructural investigations of Afzelius and colleagues. However, each discovery appears to generate additional questions. This is indicative of the importance of the subject to both basic and clinical science and of the vitality of the investigators in this field as a comprehensive understanding of ciliary diseases is sought.

Adenovirus infections and respiratory illnesses in children in group day care

Adenovirus infections and respiratory illnesses among 123 children attending a research day care center were analyzed from data collected prospectively from 1967 through 1981. During the 15-year study period, 298 adenovirus isolates were recovered from respiratory secretions of the study children, and five different serotypes were identified, with types 1, 2, and 5 accounting for 92% of the typed isolates. Annual incidence of each serotype varied greatly, with types 2 and 5 predominating before 1975 and type 1 thereafter. Exposure to adenovirus in the day care center correlated with acquisition of infection. Through two years of age, children were exposed to 3.4 +/- 0.9 (mean +/- SD) different serotypes and became infected by 2.1 +/- 0.8 different types. Most infections occurred before the child's second birthday, and incidence was highest from six to 12 months of age (1.4 primary infections/child-year). Mild and febrile illness accompanied 75% of primary isolations. Otitis media occurred in 37% of illnesses over all ages and in greater than 50% of illnesses among infants.

A Mycoplasma genitalium protein resembling the Mycoplasma pneumoniae attachment protein

In previous studies with hyperimmune rabbit sera and monoclonal antibodies against the P1 protein of Mycoplasma pneumoniae, we obtained evidence of a shared antigenic determinant with a single protein of Mycoplasma genitalium. Because of biologic and morphologic similarities between these two human Mycoplasma species, attempts were made to characterize this cross-reacting protein of M. genitalium (designated MgPa). The protein was surface exposed and had an estimated molecular size of 140 kilodaltons. Electron microscopy with monoclonal antibodies produced against either MgPa or P1 demonstrated that MgPa is located over the surface of the terminal structure of M. genitalium which is covered by a nap layer. These immunologic and morphologic findings suggest that the MgPa protein of M. genitalium could be the counterpart of the P1 protein of M. pneumoniae.

Hemophilus influenzae meningitis in the rat: behavioral, electrophysiological, and biochemical consequences

Hemophilus influenzae is the most common cause of bacterial meningitis in children, and a high percentage of survivors are at risk for long-term sequelae. To explore the mechanisms responsible for these sequelae, a neonatal rat model was used to define the behavioral, electrophysiological, and biochemical changes following meningitis. Three days after inoculation of 6-day-old rats with a minimum of 1 X 10(7) colony-forming units of a virulent Hemophilus influenzae, type b, cerebrospinal fluid and blood were cultured to confirm the presence of meningitis and bacteremia, respectively. At this time, forebrain norepinephrine and dopamine levels were significantly elevated in meningitic rats when standardized on a wet-weight basis. No changes in brain serotonin or heart norepinephrine levels could be found in the 9-day-old rats. No residual changes were found in steady-state concentrations of norepinephrine or dopamine in surviving adult rats. However, survivors that had had meningitis as neonates showed significant impairment in active and passive avoidance learning tasks and demonstrated a significantly higher level of activity during a habituation period in circular photocell activity cages. No change in the flinch-jump threshold was detected. Brainstem auditory evoked potentials showed delays of various waves in 3 of 10 Hemophilus influenzae type b-treated adult rats tested. These rats also exhibited markedly augmented locomotory responses to d-amphetamine (1 mg/kg), suggesting a long-lasting perturbation of central monoamine neuronal transmission.

Features of developing ferret tracheal epithelium: ultrastructural observations of in vivo and in vitro differentiation of ciliated cells

Ultrastructural features of the developing, surface epithelium of ferrets from birth to 28 days of age were characterized. Progressive ciliogenesis in vivo was observed, beginning with cells covering the membranous portion of the trachea. Emerging cilia appeared in ultrathin sections and by scanning electron microscopy at sites correlating with accumulation of integral membrane particles seen in freeze-fracture preparations. Two patterns of ciliogenesis were observed: (1) the random emergence of cilia over the apical cell surface, and (2) initial emergence of cilia at the peripheral boundary of the luminal border of individual cells. Novel, ringlike structures were observed on the surfaces of nonciliated cells at all ages studied. Active ciliogenesis as well as the appearance of ring structures also were documented in the superficial epithelium from 1- to 5-day-old animals maintained in vitro for up to 4 days.

Otitis media in early childhood and its relationship to later verbal and academic performance

The relationship between the occurrence of otitis media with effusion during the first 3 years of life and subsequent verbal and academic performance was examined in 61 socioeconomically disadvantaged children who attended a research day-care program. Study children were participants in a longitudinal study of child development in which the number of episodes of otitis media and duration of each otitis episode were reported prospectively from infancy. The incidence of otitis media was highest during the first 2 years of life. Bilateral otitis media accounted for 66% of the days with otitis media with effusion. Standardized tests of intelligence and academic performance were administered to the children when they were 3 1/2 to 6 years of age. No evidence of associations between measures of early childhood otitis media experience and these measures of verbal or academic functioning was found in this study population.

Acute respiratory infections in day care

A 16-year, longitudinal study of acute respiratory infections was conducted in a day care center. The incidence of infections peaked in the second six months of life (10 per child per year) and declined thereafter. Fewer than 10% of infections involved the lower respiratory tract. The isolation of respiratory viruses was associated closely with illnesses, and viruses appeared to be the most important causes of respiratory infections. Haemophilus influenzae type b was isolated infrequently and caused no invasive disease. Nontypable H. influenzae and Streptococcus pneumoniae were isolated frequently but were not associated epidemiologically with illnesses. Group A streptococci were isolated with moderate frequency but were not a major problem. Although the data presented are an inadequate basis for firm conclusions, they suggest that the incidence of acute respiratory infections during the first year of life is higher among children in day care centers than among those cared for at home but that the incidence in later years is perhaps lower for children who enter day care as infants and remain in day care through the preschool years.

Postnatal development of tracheal surface epithelium and submucosal glands in the ferret

We explored the usefulness of the postnatal ferret as a model for early developmental events in the large airways, using light and scanning electron microscopy. In the first 28 postnatal days, ferret tracheal surface epithelium and glands undergo dramatic growth and development. Tracheal surface area increases 8-fold. At birth, ciliated cells are sparse (9.4 +/- 1.2% of total epithelial cells). A significant increase in ciliated cells is observed at weekly intervals and by day 28 the ciliated cell is the predominant cell type (54.2 +/- 2.8% of total epithelial cells). Secretory cells decrease from 66.4 +/- 1.0% at birth to 22.2 +/- 2.8% of total epithelial cells. Histochemical staining of the granules of the epithelial secretory cells changes from predominantly non-acidic (staining with PAS but not Alcian blue) to predominantly acidic (staining also with Alcian blue). During the same time interval, tracheal glands develop from intraepithelial cellular aggregates devoid of secretory granules at birth into complex, submucosal tubuloacinar structures composed predominantly of cells containing non-acidic secretory granules at 28 days. Therefore, infant ferrets offer an opportunity to examine the structural and functional components of the mucociliary clearance mechanism at developmental stages which occur prenatally in many laboratory animals and in humans.

New observations on the ultrastructure of mammalian conducting airway epithelium: application of liquid propane freezing, deep etching, and rotary shadowing techniques to freeze-fracture

Freshly isolated, viable hamster tracheal epithelium was rapidly frozen in a jet of liquid nitrogen-cooled propane followed by freeze-fracture, deep etching, and rotary shadowing. Examination of the replicas by transmission electron microscopy revealed characteristic features of both ciliated and nonciliated cells, profiles of tight junctional complexes, and two distinct types of membrane particle complexes. The findings of this study suggest that rapid freezing of viable biological specimens coupled with freeze-fracture, deep etching, and rotary shadowing may provide a useful approach to achieving some additional perspectives of cell structure and function. Since the experimental protocol avoided any use of chemical fixation and processing procedures generally employed in electron microscopy, this study also validates for airway epithelium the details of fine structure observed using more conventional ultrastructural methods.

The changing pathogenicity of Mycoplasma pneumoniae with passage in vitro. Correlates of virulence

An avirulent strain of Mycoplasma pneumoniae isolated by broth passage failed to produce pneumonia in hamsters. The major biological property lost in this avirulent strain is its ability to attach to the respiratory epithelium. Although the surface protein responsible for the specific attachment of virulent M. pneumoniae has been identified, protein analysis by gel electrophoresis has failed to produce evidence that could account for the loss of virulence in the avirulent strain. It is possible that the binding sites of the avirulent strain have been altered by mutational event(s) without affecting the molecular weight or electrophoretic mobility of this protein. Antigenic determinant analysis of the membrane proteins by the use of monoclonal antibodies is suggested as a relevant approach, which may lead to a better understanding of the molecular basis of attachment.

Acquired ciliary defects in nasal epithelium of children with acute viral upper respiratory infections

Ciliary function and mucociliary clearance are primary mechanisms of defense in the respiratory tract. We found that infections by several common respiratory viruses in children were associated with ciliary abnormalities that could be detected on ultrastructural examination of the nasal epithelium. Dysmorphic ciliary forms involving microtubular aberrations were observed most often in the early stages of illness in focal sites of the nasal mucosa. Normal epithelial organization and ciliary ultrastructure appeared to be reestablished during the convalescent period, from 2 to 10 weeks after infection. These observations suggest that interference with ciliogenic mechanisms leading to transient, compromised mucociliary clearance may represent a fundamental pathophysiologic disturbance in some respiratory viral infections.

Rotary-shadowed freeze-fracture replicas: a simple method for the analysis of fracture faces

In rotary-shadowed freeze-fracture replicas, intramembrane particles on the periphery of a membrane fracture face are not uniformly shadowed from all sides. Those eccentrically positioned intramembrane particles with a net centripetally directed shadowing are on a convex fracture face. In contrast, those eccentrically positioned intramembrane particles with a net centrifugally directed shadowing are on a concave fracture face. Centrally positioned intramembrane particles on convex faces are uniformly shadowed from all sides; however, central depressions of concave faces are often unshadowed.

Conservation of pathogenic mycoplasma antigens

The protein profiles of different mycoplasmas are generally species-specific; however, several pathogenic species share certain biologic properties and/or virulence factors. We compared species of human, avian and animal origin to determine if there was evidence for conservation of key antigens. Log-phase cultures of Mycoplasma pneumoniae, M. genitalium, M. gallisepticum and M. pulmonis were subjected to SDS-gel electrophoretic analysis. Protein profiles were compared with silver-stained gels. To examine antigenic cross-reactivity, Western blots were prepared by transferring separated proteins to nitrocellulose filters and incubating these with homotypic and heterotypic antisera. Localization of cross-reacting antigens was done by immunoradioautography using 125I-labeled antiglobulins. Several two-way cross-reactions were observed among M. pneumoniae, M. genitalium, and M. gallisepticum; M. pulmonis shared no significant cross-reactions with the other three species. Preliminary evidence suggests that the cross-reactivity was due to conservation of certain antigenic determinants, although the overall protein composition of the four species was different.

Serological comparison of virulent and avirulent Mycoplasma pneumoniae by monoclonal antibodies

An avirulent strain (M129-B175) of Mycoplasma pneumoniae is morphologically indistinguishable from its virulent parent strain (M129-B7). Functionally, the avirulent strain has lost its ability to attach to respiratory epithelium and does not produce pneumonia in hamsters. Biochemical analyses by one- or two-dimensional SDS-gel electrophoresis have so far failed to produce evidence that could account for the changes in the avirulent strain. It is possible that proteins of the avirulent strain have been altered by spontaneous mutations to nonfunctional states, events which would not necessarily alter their physical properties, i.e., molecular weight. To examine this possibility, Western blots prepared from proteins of the avirulent strain, separated on SDS-gels, were exposed to a collection of monoclonal antibodies to the virulent strain. Immunoradioautographs showed that two protein bands of the avirulent strain lost their reactivity to the monoclonal antibodies, although overall protein profiles were identical. This preliminary observation suggests that spontaneous mutations that lead to structural changes in protein molecules occurred during the derivation of the avirulent strain.

Comparison of the pathogenesis of murine cytomegalovirus in lung and liver following intraperitoneal or intratracheal infection

This study compares the pathogenesis of murine cytomegalovirus (MCMV) infections following intraperitoneal (i.p.) and intratracheal (i.t.) inoculation. No deaths were seen in mice given 10(6) p.f.u. MCMV i.t., whereas 52% mortality occurred among animals given this dose i.p. This difference in mortality was not due to different effects on the lung, since virus titres in this organ on progressive days post-infection were similar for the two routes of inoculation and similar, minor histopathological changes were observed. In contrast, virus titres in the livers of mice inoculated i.p. were 100-fold higher than for those inoculated i.t., and histopathological changes were noticeably greater in the i.p. group. This suggests that the mortality seen following i.p. inoculation may have been due, at least in part, to effects of viral infection on liver function. Parallels between various forms of human cytomegalovirus infections and the types of infections seen following i.t. and i.p. infection with MCMV were observed.

Attachment by mycoplasmas and its role in disease

Mycoplasmas are the smallest free-living organisms that will grow on lifeless media. It has been demonstrated that these organisms are extracellular parasites in both animal and human diseases and that they attach to mucosal surfaces. Some of the mycoplasma species have differentiated, terminal attachment organelles. A definitive characterization of host-cell receptors and the binding sites on mycoplasmas should aid in the understanding of disease mechanisms. This information may then be used to develop strategies for prevention of diseases due to mycoplasmas.

A solid-phase radioimmunoassay for detection of antibodies against Mycoplasma pneumoniae

A solid-phase radioimmunoassay (RIA) for the detection of Mycoplasma pneumoniae antibodies is described. This method uses M. pneumoniae organisms grown in microtiter plate wells as a solid-phase antigen that is economical and easy to prepare. Results obtained from our studies indicate this RIA method is highly sensitive and reproducible. This is a more specific assay than the popular complement fixation (CF) method because the glycolipid haptens employed in the CF test are not unique to M. pneumoniae. Data on 34 serum samples from 12 patients indicate the applicability of this diagnostic method for clinical use. In addition, this method measures the immunoglobulin class-specific antibody activities which may be important in differentiating recent and past infections.

Demonstration of antibodies to Mycoplasma pneumoniae attachment protein in human sera and respiratory secretions

Antibodies specific to the attachment protein of Mycoplasma pneumoniae were demonstrated in sera and respiratory secretions of human patients. The results indicate that the attachment protein is a major immunogen.

Croup: an 11-year study in a pediatric practice

The etiology and epidemiology of croup were studied in a pediatric group practice over an 11-year period, 1964 to 1975. Croup was diagnosed in 951 instances in 6,165 cases of lower respiratory tract infection (LRI) studied. As census figures of the practice clientele were available, attack rates were calculated. The incidence of total LRI was highest in the first year of life. In contrast, the attack rate for croup was highest in the second year of life; the rate declined gradually after that age. Croup was not diagnosed in the first month of life. Boys were 1.43 times more likely to develop croup than were girls. Three hundred sixty agents were isolated from the 951 croup cases. The parainfluenza viruses accounted for 74.2% of all isolates; 65% of the parainfluenza isolates were classified as parainfluenza virus type 1. Respiratory syncytial virus, influenza viruses A and B, and Mycoplasma pneumoniae were the only other agents isolated in appreciable numbers. The propensity of various agents to produce croup symptoms in children with LRI due to specific microorganisms was 58% for parainfluenzae type 1,60% for parainfluenzae type 2, and 29% for parainfluenzae type 3; similar figures for the other agents varied from 5% to 16%. The role of the various agents in the etiology of croup varied with patient age and depended on the propensity of the agent to produce the croup syndrome and the frequency of isolation of the agent at that age. The parainfluenza viruses were the most important croup agents at all ages; respiratory syncytial virus caused croup in children less than 5 years of age whereas the influenza viruses and M pneumoniae were significant causes of croup only in children more than 5 to 6 years old. Croup occurred predominately in late fall and early winter, times when the parainfluenza viruses, especially type 1, occurred most frequently. The epidemiology of croup differs from that of bronchiolitis, pneumonia, and tracheobronchitis; knowledge of this should be helpful to the clinician caring for children with LRI.

Location of attachment moiety on Mycoplasma pneumoniae

Mycoplasma pneumoniae initiates infection in the human host by attachment to respiratory epithelium. The organism attaches by a specialized terminal structure. Monoclonal antibodies to an organism surface protein (P1) inhibited attachment to respiratory epithelium and were localized to the tip structure by a ferritin antibody label. The P1 protein was degraded by trypsin treatment to smaller polypeptides that possessed the same antigenic determinants as the larger P1 protein when reacted with the specific monoclonal antibody, and evidence has been provided for the existence of multiple antigenic determinants on the attachment protein.

Congenital toxoplasmosis associated with acquired oculomotor nerve (CN III) palsy

A nine-week-old Caucasian male presented with right ptosis and right exotropia due to a third cranial nerve palsy. Symmetrical macular lesions and a paramacular hyperpigmented lesion with overlying vitreous cells in the left eye were compatible with congenital toxoplasmosis. Computer tomography demonstrated calcifications in the periventricular and midbrain regions where the oculomotor nerve exits the brainstem. The diagnosis was confirmed by the toxoplasma indirect fluorescent antibody titer greater than 1:2048 for the infant and greater than 1:512 for the mother. Treatment was instituted with pyrimethamine, sulfadiazine and folinic acid. Neurologic sequelae included a right hemiparesis, infantile seizures, and generalized developmental delay. A Mueller's muscle resection (RUL) combined with 9-mm recession of the right lateral rectus and 7-mm resection of the right medial rectus muscles produced minimal ptosis and right exotropia one year later. the child now prefers to fix with the right eye and a vertical nystagmus is evident in the left eye. To our knowledge this is the first reported case of an infant with noncomitant strabismus due to congenital toxoplasma cranial nerve involvement. The finding of an acquired third cranial nerve palsy accompanied by progressive neurologic sequelae warrants consideration of congenital toxoplasmosis.

A longitudinal study of respiratory viruses and bacteria in the etiology of acute otitis media with effusion

We analyzed data from a 14-year longitudinal study of respiratory infections in young children to determine the relative importance of viral respiratory infection and nasopharyngeal colonization with Streptococcus pneumoniae and Haemophilus influenzae as factors influencing the occurrence of acute otitis media with effusion. The incidence of this disorder was increased in children with viral respiratory infections (average relative risk, 3.2; P less than 0.0001). Infection with respiratory syncytial virus, influenza virus (type A or B), and adenovirus conferred a greater risk of otitis media than did infection with parainfluenza virus, enterovirus, or rhinovirus. Colonization of the nasopharynx with Str. pneumoniae or H. influenzae had a lesser effect on the incidence of the disease (average relative risk; 1.5; P less than 0.01). Infections with the viruses more closely associated with acute otitis media (respiratory syncytial virus, adenovirus, and influenza A or B) were correlated with an increased risk of recurrent disease. Prevention of selected otitis-associated viral infections should reduce the incidence of this disease.

Long-term mouse cytomegalovirus infection of tracheal organ culture: relation to host cell replication

Tracheal organ cultures infected with mouse cytomegalovirus (MCMV) were shown to produce virus for up to 180 days with virus replication primarily in epithelial cells. Persistent virus infections were established in tracheal organ cultures from both MCMV-susceptible and MCMV-resistant strains of mice. In acutely infected tracheal organ cultures, cellular DNA synthesis appeared to precede the production of significant amounts of virus antigens and the release of virus into culture fluids. Since persistently infected tracheal organ cultures continued to synthesize cellular DNA, the results suggest that host cell turnover may continually renew the population of MCMV-susceptible cells. The results suggest a possible mechanism for virus persistence in tracheal organ culture based on continuing serial infection of newly susceptible cells combined with prolonged release of virus infected cells.

Host-pathogen interactions in experimental Mycoplasma pneumoniae disease studied by the freeze-fracture technique

The application of freeze-fracture and organ culture technology to the study of disease caused by Mycoplasma pneumoniae provided a new perspective on host-pathogen interactions. Structural variations of the M. pneumoniae membrane and alterations of the host cell membrane that are induced by this pathogen during experimental infection were observed. Study of freeze-fracture preparations of M. pneumoniae revealed the presence of numerous membrane-associated particles embedded in the inner aspect of the bimolecular leaflet. However, areas of the fractured membrane of cells sometimes had particle-free zones and/or blebs. These particle-free areas were sometimes closely aligned to host tracheal epithelium in organ culture. In addition, marked changes in the membrane integrity of the host epithelium during experimental infection were observed. Deterioration of luminal surface membranes and alterations in the distribution of ciliary intramembranous particles were frequently noted. Ciliary dysfunction was also suggested by observations of abnormally aligned and clumped adjacent cilia. These findings correlated well with biochemical data demonstrating altered host macromolecular synthesis and observations of ciliostasis during experimental M. pneumoniae infection.

Attachment of Mycoplasma pneumoniae to hamster tracheal organ cultures, tracheal outgrowth monolayers, human erythrocytes, and WiDr human tissue culture cells

Virulent strains of Mycoplasma pneumoniae, PI-1428 and M129, were radiolabeled wtih [3H]palmitic acid or [3H]thymidine and examined for attachment to hamster tracheal organ cultures, tracheal outgrowth monolayers, human O-positive erythrocytes, and human WiDr carcinoma cell cultures. Although attachment to each cell substrate was readily detected, the WiDr cell culture monolayers provided the most satisfactory substrate for quantitating mycoplasma attachment. Serious technical limitations were encountered with each of the other substrates that we examined; these limitations interfered with reproducibility or sensitivity and rendered tracheal organ cultures and erythrocyte suspensions unsuitable for routine attachment and attachment inhibition assays. Moreover, the WiDr cell monolayer was the most sensitive substrate for determining attachment inhibition activity in protein-containing extracts prepared from M. pneumoniae. The significance of these findings is discussed.

The epidemiology of tracheobronchitis in pediatric practice

Epidemiologic characteristics of childhood tracheobronchitis occurring over a 104-month period in Chapel Hill, NC, were ascertained and compared to those of other pediatric lower respiratory illness (LRI) syndromes. Tracheobronchitis accounted for 40% of all LRI seen at the community's only pediatric practice. Tracheobronchitis incidence was highest during the first two years of life, through the ratio of tracheobronchitis incidence to total LRI incidence increased with age. A viral pathogen or Mycoplasma pneumoniae was isolated from 23% of tracheobronchitis cases; the agents most commonly isolated were parainfluenza viruses, influenza viruses, respiratory syncytial virus, and M. pneumoniae. Influenza virus, particularly type B, was isolated more commonly in tracheobronchitis than in other LRI syndromes. Over all age groups, peak incidence of tracheobronchitis, like that of pneumonia and bronchiolitis, occurred during the winter months. In school-age children, however, tracheobronchitis incidence was more likely than that of other syndromes to be elevated in late winter or early spring, when several influenza B outbreaks occurred in Chapel Hill. Available evidence suggests that risk of chronic respiratory disease is related inversely to age at which acute respiratory infection first occurs, and that a component of wheezing may not be required to confer such risk. These considerations, coupled with the high incidence of tracheobronchitis early in life, warrant further description of this syndrome and assessment of its implications.