Enhancement of monoclonal antibody production by immobilized hybridoma cell culture with hyperosmolar medium

To determine the effect of hyperosmotic stress on the monoclonal antibody (MAb) production by calcium-alginate-immobilized S3H5/gamma2bA2 hybridoma cells, the osmolalities of medium in the MAb production stage were varied through the addition of NaCI. The specific MAb productivity (q(MAb)) of immobilized cells exposed to abrupt hyperosmotic stress (398 mOsm/kg) was increased by 55% when compared with that of immobilized cells in the control culture (286 mOsm/kg). Furthermore, this enhancement of q(MAb) was not transient. Abrupt increase in osmolality, however, inhibited cell growth, resulting in no increase in volumetric MAb productivity (r(MAb)). On the other hand, gradual increase in osmolality allowed further cell growth while maintaining the enhanced q(MAb) immobilized cells. The q(MAb) immobilized cells at 395 mOsm/kg was 0.661 +/- 0.019 mug/10(6) cells/h, which is almost identical to that of immobilized cells exposed to abrupt osmotic stress. Accordingly, the r(MAb) was increased by ca. 40% when compared with that in the control immobilized cell culture. This enhancement in i(MAb) of immobilized S3H5/gamma2bA2 hybridoma cells by applying gradual osmotic stress suggests the potential of using hyperosmolar medium in other perfusion culture systems for improved MAb production. (c) 1995 John Wiley & Sons, Inc.

Clonal replacement among 19A Streptococcus pneumoniae in Massachusetts, prior to 13 valent conjugate vaccination

As part of an ongoing study of the response of the Streptococcus pneumoniae population to conjugate vaccination, we applied multi-locus sequence typing (MLST) to 291 isolates sampled from nasopharyngeal carriage in Massachusetts children. We found 94 distinct sequence types (STs), including 19 that had not been previously recorded, and a xpt allele containing a large insertion. Comparison with a similar sample collected in 2007 revealed no significant overall difference in the ST composition (p=0.51) suggesting that the population has reached a new equilibrium following the introduction of 7 valent vaccination in 2000. Within serotypes, a large and statistically significant increase (p=0.014 Fisher's Exact test) was noted in the prevalence of the major multiresistant clone ST 320, which is apparently outcompeting ST 199 among serotype 19A strains. This sample will be used as a baseline to study the future evolution of the pneumococcal population in Massachusetts following introduction of vaccines with higher valency.

Effect of hypoosmotic pressure on cell growth and antibody production in recombinant Chinese hamster ovary cell culture

To determine the response of recombinant Chinese hamster ovary (rCHO) cells subjected to hypoosmotic pressure, rCHO cells (CS13*-1.0) producing a chimeric antibody were cultivated in the hypoosmolar medium resulting from NaCl subtraction. At hypoosmotic pressure, CS13*-1.0 cells displayed decreased specific growth rate (mu) and increased specific antibody productivity (q (Ab)).When the medium osmolality was decreased from 300 mOsm kg(-1)(physiological osmolality) to 150 mOsm kg(-1), mu was decreased by 68% and q (Ab) was increased by 128%. To understand the mechanism of enhanced q (Ab) resulting from hypoosmotic pressure, cellular responses of cells in the exponential phase of growth were observed at the transcription level. Total cytoplasmic RNA content per cell at 150 mOsm kg(-1) was increased by 140%, compared with that at 300 mOsm kg(-1). On a per mug RNA basis, immunoglobulin (Ig) mRNA levels at 150 mOsm kg(-1) were comparable to those at 300 mOsm kg(-1), indicating that hypoosmotic pressure did not lead to the preferential transcription of Ig mRNAs. Taken together, the data obtained here suggest that the increase in total RNA pool is primarily responsible for the enhanced q (Ab) of CS13*-1.0 cells subjected to hypoosmotic pressure.

Comparison of gene expression profile between human chondrons and chondrocytes: a cDNA microarray study

OBJECTIVE

The chondron is a basic unit of articular cartilage that includes the chondrocyte and its pericellular matrix (PCM). This current study was designed to investigate the effects of the chondron PCM on the gene expression profile of chondrocytes.

DESIGN

Chondrons and chondrocytes were enzymatically isolated from human articular cartilage, and maintained in pellet culture. Pellets of chondrons or chondrocytes were collected at days 1, 3 and 5 for cDNA microarray analysis.

RESULTS

In comparison with chondrocytes alone, chondrons had 258 genes, in a broad range of functional categories, either up- or downregulated at the three time points tested. At day 1, 26 genes were significantly upregulated in chondrons and four downregulated in comparison to chondrocytes. At day 3, the number of upregulated chondron genes was 97 and the number downregulated was 43. By day 5, there were more downregulated genes (56) than upregulated genes (32) in chondrons. Upregulation of a group of heat shock proteins (HSPA1A, HSPA2 and HSPA8) in chondrons was validated by real time reverse transcription polymerase chain reaction (RT-PCR). Genes related to chondrocyte hypertrophy and dedifferentiation such as SSP1 and DCN were downregulated in chondrons as compared to the expression in chondrocytes.

CONCLUSION

The presence of the PCM in chondrons has a profound influence on chondrocyte gene expression. Upregulation of the heat shock protein 70 may contribute to the robustness and active matrix production of chondrons. The intact PCM may further stabilize the phenotype of chondrocytes within chondrons.

Yeast hydrolysate as a low-cost additive to serum-free medium for the production of human thrombopoietin in suspension cultures of Chinese hamster ovary cells

To enhance the performance of a serum-free medium (SFM) for human thrombopoietin (hTPO) production in suspension cultures of recombinant Chinese hamster ovary (rCHO) cells, several low-cost hydrolysates such as yeast hydrolysate (YH), soy hydrolysate, wheat gluten hydrolysate and rice hydrolysate were tested as medium additives. Among various hydrolysates tested, the positive effect of YH on hTPO production was most significant. When 5 g l(-1) YH was added to SFM, the maximum hTPO concentration in batch culture was 40.41 microg ml(-1), which is 11.5 times higher than that in SFM without YH supplementation. This enhanced hTPO production in YH-supplemented SFM was obtained by the combined effect of enhanced q(hTPO) (the specific rate of hTPO production). The supplementation of YH in SFM increased q(hTPO) by 294% and extended culture longevity by >2 days if the culture was terminated at a cell viability of 50%. Furthermore, cell viability throughout the culture using YH-supplemented SFM was higher than that using any other hydrolysate-supplemented SFM tested, thereby minimizing degradation of hTPO susceptible to proteolytic degradation. In addition, YH supplementation did not affect in vivo biological activity of hTPO. Taken together, the results obtained demonstrate the potential of YH as a medium additive for hTPO production in serum-free suspension cultures of rCHO cells.

A neocartilage ideal for extracellular matrix macromolecule immunolocalization

A neocartilage construct readily amenable to microscopy and biomechanical studies is described. Porcine articular cartilage was digested with a mixture of dispase and collagenase for chondrons or pronase and collagenase for chondrocytes. Chondrons or chondrocytes plated in 96-well plates were fixed and immunolabeled in situ for fluorescence microscopy at days 4 and 11. Collagen types I and II, aggrecan, and MMP-13 expression was assayed by semiquantitative RT-PCR. Cell numbers were analyzed by MTT assay. Chondrons and chondrocytes produced neocartilage that could be handled with minimal tearing on day 3 and none on day 11. Some cell division occurred between days 4 and 7. In both cultures, chondrocytes were surrounded by a thin rim of type VI collagen and osteopontin. Type II collagen, keratan sulfate, and tenascin were abundant throughout. At day 3, cells were rounded but by day 11 flattened cells were visible in the substratum. Continued synthesis of aggrecan and type II collagen mRNA indicated maintenance of the chondrocyte phenotype. The neocartilage was easy to immunolabel in situ without the need for sectioning, and individual cells were readily observed by microscopy. The versatility of these constructs makes them ideal for microscopy and for biomechanical studies.

Effects of cloned gene dosage on the response of recombinant CHO cells to hyperosmotic pressure in regard to cell growth and antibody production

The effect of cloned gene dosage on growth and product formation under hyperosmotic conditions has been studied using recombinant Chinese hamster ovary (rCHO) cell lines producing chimeric antibody. Batch cultures of four rCHO cell lines carrying different numbers of antibody gene copies were carried out using the hyperosmolar medium. Depending on cloned gene dosage, hyperosmotic pressure decreased specific growth rate (mu) and increased specific antibody productivity (q(Ab)) to a different degree. The cell line with lower cloned gene dosage displayed more significant enhancement in q(Ab) and less reduction in mu at hyperosmolalities. However, the cell line with higher cloned gene dosage still yielded higher maximum antibody concentration at hyperosmolality up to 469 mOsm/kg. Northern blot analysis showed a positive relationship between immunoglobulin mRNA level per cell and q(Ab), indicating that transcriptional regulation was involved in the response of rCHO cells to hyperosmotic pressure. Cell cycle analysis showed that hyperosmotic pressure induced G(1)-phase arrest, suggesting that the increase of cell population in G(1)-phase may contribute in part to enhanced q(Ab) at hyperosmolality. Taken together, although the cell line with lower cloned gene dosage displayed more significant enhancement in q(Ab) at hyperosmolality, the factor that determined the maximum antibody concentration in hyperosmotic rCHO cell cultures was almost exclusively the gene dosage.

Management of febrile children in the age of the conjugate pneumococcal vaccine: a cost-effectiveness analysis

OBJECTIVES

The optimal practice management of highly febrile 3- to 36-month-old children without a focal source has been controversial. The recent release of a conjugate pneumococcal vaccine may reduce the rate of occult bacteremia and alter the utility of empiric testing and treatment. The objective of this study was to determine the cost-effectiveness of 6 different management strategies of febrile 3- to 36-month-old children at current and declining rates of occult pneumococcal bacteremia.

METHODS

A cost-effectiveness (CE) analysis was performed to compare the strategies of "no work-up," "clinical judgment," "blood culture," "blood culture + treatment," "complete blood count (CBC) + selective blood culture and treatment," and "CBC and blood culture + selective treatment." A hypothetical cohort of 100 000 children who were 3 to 36 months of age and had a fever of >/=39 degrees C and no source of infection was modeled for each strategy. Our main outcome measures were cases of meningitis prevented, life-years saved compared with "no work-up," total cost (1999 dollars), and incremental CE ratios.

RESULTS

When compared with "no work-up," the strategy of "CBC + selective blood culture and treatment" using a white blood cell (WBC) cutoff of 15 x 10(9)/L prevents 48 cases of meningitis, saves 86 life-years per 100 000 patients, and is less costly at the current rate of bacteremia (1.5%). Using the strategy of "CBC + selective blood culture and treatment" with a lower WBC cutoff of 10 x 10(9)/L costs an additional $72 300 per life-year saved. If the rate of bacteremia declines to 0.5%, then the incremental CE ratio of "clinical judgment" compared with "no work-up" is $38 000 per life-year saved; however, strategies that include empiric testing or treatment result in CE ratios greater than $300 000 per life-year saved.

CONCLUSIONS

"CBC + selective blood culture and treatment" using a WBC cutoff of 15 x 10(9)/L is cost-effective at the current rate of pneumococcal bacteremia. If the rate of occult bacteremia falls below 0.5% with widespread use of the conjugate pneumococcal vaccine, then strategies that use empiric testing and treatment should be eliminated.

Domain and genomic sequence analysis of bdellin-KL, a leech-derived trypsin-plasmin inhibitor

Bdellin-KL is a trypsin-plasmin inhibitor from Hirudo nipponia, whose N-terminal sequence was identified as a non-classical Kazal-type. A cDNA clone encoding the inhibitor was isolated by reverse transcription-PCR and 5' rapid amplification of cDNA ends. The cDNA showed an open reading frame of 155 amino acids comprising one signal peptide and two separated domains. The C-terminal domain consists of distinct internal repeats, including HHEE and HHDD. The bdellin-KL sequence, from the constructed genomic library of Korean leech, was determined for the 2109 bases comprising the open reading frame and flanking regions (3' and 5'). The promoter region contains potential regulatory sequence motifs, including TATA, CAAT, and GC boxes. To characterize the properties of each domain, an N-terminal fragment was prepared by limited proteolysis of the intact protein. The inhibitory activity of the region was as potent as that of the intact protein. This suggests that the compact domain plays an important part in the inhibitory action of bdellin-KL. The C-terminal domain was revealed to have binding affinity to ions such as Ca(2+), Zn(2+), Fe(3+), and Fe(2+) without an influence on the inhibitory activity. This study demonstrates that bdellin-KL may be a novel bifunctional protein with two distinct domains.

ATP induces Ca(2+) signaling in human chondrons cultured in three-dimensional agarose films

OBJECTIVE

In vivo, chondrocytes are surrounded by an extracellular matrix, preventing direct cell-to-cell contact. Consequently, intercellular communication through gap junctions is unlikely. However, signaling at a distance is possible through extracellular messengers such as nitric oxide (NO) and nucleotides and nucleosides, adenosine triphosphate (ATP), uridine triphosphate (UTP), or adenosine diphosphate (ADP). We hypothesized that chondrons, chondrocytes surrounded by their native pericellular matrix, increase their intracellular calcium concentration ([Ca(2+)]ic) in response to ATP and other signaling molecules and that the source of Ca(2+) is from intracellular stores. The objectives of this study were to determine if chondrons in a 3-D gel respond to ATP by increasing [Ca(2+)]ic through a purinoceptor mechanism and to test whether chondrons in whole tissue samples would respond to ATP in a similar fashion.

DESIGN

Human chondrons, cultured in a three-dimensional agarose gel or in whole cartilage loaded with Fura-2AM, a calcium sensitive dye, were stimulated with 1, 5 and 10 microM ATP. A ratio-imaging fluorescence technique was used to quantitate the [Ca(2+)]ic.

RESULTS

ATP-stimulated chondrons increased their [Ca(2+)]ic from a basal level of 60 nM to over 1000 nM. Chondrons incubated in calcium-free medium also increased their [Ca(2+)]ic in response to ATP, indicating the source of Ca(2+) was not extracellular. ATP-induced calcium signaling was inhibited in chondrons pre-treated with suramin, a generic purinoceptor blocker. In addition, UTP and adenosine 5'-O-(3-thiotriphosphate) (ATPgammas) induced a calcium response, but 2-methylthio-ATP (2-MeSATP), ADP, and adenosine did not induce a significant increase in [Ca(2+)]ic, substantiating that the P2Y2 purinoceptor was dominant. Chondrons in whole cartilage increased [Ca(2+)]ic in response to ATP.

CONCLUSIONS

We conclude that chondrons in 3-D culture respond to ATP by increasing [Ca(2+)]ic via P2Y2 receptor activation. Thus, ATP can pass through the agarose gel and the pericellular matrix, bind purinoceptors and increase intracellular Ca(2+) in a signaling response.

Overexpression of bcl-2 inhibits sodium butyrate-induced apoptosis in Chinese hamster ovary cells resulting in enhanced humanized antibody production

Sodium butyrate (NaBu) can enhance the expression of genes from some of the mammalian promoters including cytomegalovirus (CMV) and simian virus 40 (SV40), but it can also inhibit cell growth and induce cellular apoptosis. Thus, the beneficial effect of using a higher concentration of NaBu on a foreign protein expression is compromised by its cytotoxic effect on cell growth. To overcome this cytotoxic effect of NaBu, a survival protein, human Bcl-2, was overexpressed in recombinant Chinese hamster ovary (CHO) cells (SH2-0.32), producing a humanized antibody directed against the S surface antigen of hepatitis B virus. When batch cultures of both control cells transfected with bcl-2-deficient plasmid (SH2-0.32-Deltabcl-2) and cells transfected with bcl-2 expression plasmid (14C6-bcl-2) were performed in the absence of NaBu, both cells showed similar profiles of cell viability and antibody production. Compared with the SH2-0.32-Deltabcl-2 culture, under the condition of NaBu addition at the exponential growth phase, overexpression of the bcl-2 gene considerably suppressed the NaBu-induced apoptosis of 14C6-bcl-2 by inhibiting caspase 3 activity and extending culture longevity by >2 days. As a result, the final antibody concentration of 14C6-bcl-2 culture was twofold higher than that of SH2-0.32-Deltabcl-2 culture in the presence of NaBu and threefold higher than that of SH2-0.32-Deltabcl-2 and 14C6-bcl-2 cultures in the absence of NaBu.

Orthophosphate anion enhances the stability and activity of endoxylanase from Bacillus sp

Endoxylanase, for which the optimum temperature is 60 degrees C (optimum pH 7), is labile to heat. Because the isoelectric point (pI) value of this xylanase is 10.6, the net charge of this enzyme is positive at pH 7. Thus, ions are likely to influence its enzyme structure and the thermal stability of endoxylanase may improve. Among the various ions tested, orthophosphate anion (HPO(4)(2-)) was found to significantly improve not only the stability but the activity of xylanase. When K(2)HPO(4) concentration was increased from 50 mM to 1.2 M, the T(m )value of xylanase was increased from 60.0 degrees C to 74.5 degrees C. The affinity of xylanase on xylan also increased along with K(2)HPO(4) concentration. Thus, the xylanase activity at 0.6 M K(2)HPO(4) was 2.3-fold higher than that at 50 mM K(2)HPO(4), and 120.2-fold higher than that in 40 mM MOPS buffer. This enhanced activity in the presence of K(2)HPO(4 )probably takes place because the orthophosphate anion affects the binding and catalytic residues of endoxylanase.

Key determinants in the occurrence of clonal variation in humanized antibody expression of cho cells during dihydrofolate reductase mediated gene amplification

Recombinant Chinese hamster ovary (CHO) parental clones expressing a humanized antibody against S surface antigen of hepatitis B virus were obtained by cotransfection of heavy chain (HC) and light chain (LC) cDNA expression vectors into dihydrofolate reductase (DHFR)-deficient CHO cells. When 23 representative parental clones were subjected to stepwise selection for increasing methotrexate (MTX) resistance, such as 0.02, 0.08, 0.32, and 1.0 microM, their clonal variations in regard to antibody expression were found to be significant. Among 23 parental clones, only one clone (hu17) showed the significant increment of specific antibody productivity (q(Ab)) with increasing MTX concentration up to 0.32 microM. Compared with the parental clone (hu17), the q(Ab) of hu17 resistant at 0.32 microM MTX (hu17-0.32) was enhanced approximately 12.5-fold. To clarify the reason for the occurrence of clonal variations, Southern blot analyses of chromosomal DNAs derived from each amplified clone at 0.32 microM MTX were performed. Only the hu17-0.32 clone did not experience severe genetic rearrangement during gene amplification, and it had only one 49-kb amplification unit including the LC and HC cDNAs. A fluorescent MTX competition assay showed that the resistance against MTX toxicity of the other clones without enhanced q(Ab) at 0.32 microM MTX was obtained by mechanisms such as an impaired MTX transport system. Taken together, the data obtained here show that clonal variations in regard to antibody expression are found to be significant because clones can acquire MTX resistance by mechanisms other than DHFR-mediated gene amplification despite the stepwise selection.

Viscoelastic properties of chondrocytes from normal and osteoarthritic human cartilage

The deformation behavior and mechanical properties of articular chondrocytes are believed to play an important role in their response to mechanical loading of the extracellular matrix. This study utilized the micropipette aspiration test to measure the viscoelastic properties of chondrocytes isolated from macroscopically normal or end-stage osteoarthritic cartilage. A three-parameter standard linear solid was used to model the viscoelastic behavior of the cells. Significant differences were found between the mechanical properties of chondrocytes isolated from normal and osteoarthritic cartilage. Specifically, osteoarthritic chondrocytes exhibited a significantly higher equilibrium modulus (0.33 +/- 0.23 compared with 0.24 +/- 0.11 kPa), instantaneous modulus (0.63 +/- 0.51 compared with 0.41 +/- 0.17 kPa), and apparent viscosity (5.8 +/- 6.5 compared with 3.0 +/- 1.8 kPa-s) compared with chondrocytes isolated from macroscopically normal, nonosteoarthritic cartilage. The elastic moduli and relaxation time constant determined experimentally in this study were used to estimate the apparent biphasic properties of the chondrocyte on the basis of the equation for the gel relaxation time of a biphasic material. The differences in viscoelastic properties may reflect alterations in the structure and composition of the chondrocyte cytoskeleton that have previously been associated with osteoarthritic cartilage. Coupled with earlier theoretical models of cell-matrix interactions in articular cartilage, the increased elastic and viscous properties suggest that the mechanical environment of the chondrocyte may be altered in osteoarthritic cartilage.

Osmoprotective effect of glycine betaine on foreign protein production in hyperosmotic recombinant chinese hamster ovary cell cultures differs among cell lines

When three recombinant Chinese hamster ovary (rCHO) cell lines, CHO/dhfr-B22-4, CS13-1.00*, and CS13-0.02*, were cultivated in hyperosmolar media resulting from NaCl addition, their specific foreign protein productivity increased with medium osmolality. However, due to a simultaneous suppression of cell growth at elevated osmolality, no enhancement in the maximum foreign protein titer was made in batch cultures. To test the feasibility of using glycine betaine, known as a strong osmoprotective compound, for improved foreign protein production in hyperosmotic rCHO cell cultures, hyperosmotic batch cultures were carried out in the presence of 15 mM glycine betaine. Glycine betaine was found to have a strong osmoprotective effect on all three rCHO cell lines. Inclusion of 15 mM glycine betaine in hyperosmolar medium enabled rCHO cell lines to grow at 557 to 573 mOsm/kg, whereas they could not grow in the absence of glycine betaine. However, effect of glycine betaine inclusion in hyperosmolar medium on foreign protein production differed among rCHO cell lines. CHO/dhfr-B22-4 cells retained enhanced specific human thrombopoietin (hTPO) productivity in the presence of glycine betaine, and thereby the maximum hTPO titer obtained at 573 mOsm/kg was increased by 72% over that obtained in the control culture with physiological osmolality (292 mOsm/kg). On the other hand, enhanced specific antibody productivity of CS13-1.00* and CS13-0.02* at elevated osmolality was decreased significantly in the presence of glycine betaine. As a result, the maximum antibody titer at 557 mOsm/kg was similar to that obtained in the control culture with physiological osmolality. The mRNA contents per cell determined by northern blot hybridization correlated with q in all three rCHO cell lines, indicating that transcriptional regulation is responsible in part for q enhancement at hyperosmolality in the absence as well as the presence of glycine betaine. Taken together, efficacy of the simultaneous use of hyperosmotic pressure and glycine betaine as a means to improve foreign protein production was variable among different rCHO cell lines.

Morphological selection of parental Chinese hamster ovary cell clones exhibiting high-level expression of recombinant protein

To facilitate the establishment of recombinant Chinese hamster ovary (rCHO) cell lines with dihydrofolate reductase (dhfr)-mediated gene amplification, a primary selection method based on morphology of parental CHO clones has been developed. Morphology of parental clones that were made by transfecting various plasmids encoding thrombopoietin (TPO) and its analogs and humanized antibodies into dhfr-deficient (dhfr-) CHO cells was not uniform. Morphology of many parental clones exhibiting high-level expression of the introduced gene was similar to that of nontransfected dhfr- CHO cells. On the other hand, most parental clones with low-level expression experienced noticeable morphological changes such as bipolar fibroblast-like morphology. In case of selection of parental clones with TPO expression level higher than 200 ng/mL, morphological selection improved selection efficiency by 3.5-fold compared with random selection. Furthermore, when subjected to methotrexate for gene amplification, parental clones that were selected based on morphology elevated the expression level as much as those that were selected randomly. Taken together, morphological selection of parental clones can facilitate the establishment of rCHO cell lines expressing recombinant proteins.

Justification of continuous packed-bed reactor for retroviral vector production from amphotropic PsiCRIP murine producer cell

To indentify a plausible large-scale production system forretroviral vector, three culture systems, i.e., batch culturewith medium exchange, microcarrier culture, and packed-bedreactor culture were compared. In batch cultures with mediumexchange, high cell concentrations were maintained for about amonth, and the harvested retroviral titer remained constant. Inmicrocarrier cultures, although cell growth was rapid, theretroviral titer was unexpectedly low, suggesting that the lowtiter was due either to serious damage to the retroviral vectoror to a reduction in the production rate of retroviral vector,caused by mechanical shear forces. Although the retroviral titer(maximum titer, 1.56 x 10(6)) in the packed-bedreactor was a little bit lower than that obtained in the batchculture with medium exchange (maximum titer, 1.91 x10(6)), continuous production made it possible to increasethe cumulative titer up to 16-fold of that from the batchculture with medium exchange. Moreover, as the packed-bedreactor system requires less labor and shows excellentvolumetric productivity in comparison to batch cultures withmedium exchanges, it will be an appropriate production systemfor retroviral vector in large quantities.

Epidemiology of acute viral respiratory tract infections in Korean children

OBJECTIVE

Viruses are the most common causes of respiratory tract infection in children. We investigated the aetiologies and the epidemiological features of acute viral respiratory tract infections in Korean children.

METHODS

We tried to isolate respiratory syncytial virus (RSV) and parainfluenza virus from January 1994, influenza virus from February 1995, and adenovirus from April 1996 through August 1998, and identified the isolated viruses by indirect immunofluorescence (IF) staining in the children hospitalized with acute respiratory tract infections (ARTI).

RESULTS

Virus was identified in 360 of 1389 (25.9%) nasopharyngeal aspirates cultured. Of a total of 392 viruses, 164 (41.8%) RSV, 90 (23%) parainfluenza virus, 66 (16.8%) influenza A virus, 54 (13.8%) adenovirus, and 18 (4.6%) influenza B virus were cultured, including cases in mixed viral infections. The male to female ratio of the culture-positive patients was 2:1, and the proportions of the patients aged >6 months, 6-11 months, 1, 2, 3, 4, 5, 6-7, 8-9, and >10 years were 22.5, 29.5, 25.7, 9.5, 3.8, 3.8, 1.7, 1.7, 1.2, and 0.6%, respectively. The major clinical diagnosis was bronchiolitis for RSV, croup for parainfluenza virus, and pneumonia for adenovirus and influenza virus. Infections by RSV, parainfluenza virus, and influenza virus occurred in annual epidemics, and infections by adenovirus occurred annually with or without epidemics. There were somewhat larger epidemics by adenovirus and influenza virus in May to July 1996 and March to June 1997, respectively.

CONCLUSIONS

Viral agents are one of the main aetiologies and the main causes of admission in Korean children with ARTI.

Osmoprotective effect of glycine betaine on thrombopoietin production in hyperosmotic Chinese hamster ovary cell culture: clonal variations

When 23 recombinant Chinese hamster ovary (rCHO) cell clones were cultivated in hyperosmolar medium resulting from NaCl addition (533 mOsm/kg), their specific thrombopoietin (TPO) productivity (q(TPO)) was increased. However, due to depressed cell growth at elevated osmolality, no enhancement in the maximum TPO titer was made in batch cultures of all 23 clones. To test the feasibility of using glycine betaine, known as a strong osmoprotective compound, for improved TPO production in hyperosmotic rCHO cell cultures, hyperosmotic batch cultures of 23 clones were performed in the presence of 15 mM glycine betaine. Glycine betaine was found to have a strong osmoprotective effect on all 23 clones. Inclusion of 15 mM glycine betaine in hyperosmolar medium enabled 22 clones to grow at 542 mOsm/kg, where most clones could not grow in the absence of glycine betaine, but at a cost of reduced q(TPO). However, the relative decrease in q(TPO) varied significantly among clones. Thus, efficacy of the simultaneous use of hyperosmotic pressure and glycine betaine as a means to improve foreign protein production was variable among clones. Six out of 23 clones displayed more than a 40% increase in the maximum TPO titer in the hyperosmolar medium containing glycine betaine, compared with that in the standard medium with a physiological osmolality. Taken together, the results obtained here emphasize the importance of selection of clones for the successful use of hyperosmotic pressure and glycine betaine as an economical means to improve TPO production.

The use of electric bed heaters and the risk of clinically recognized spontaneous abortion

We conducted a prospective cohort study to evaluate the relation of spontaneous abortion and electric bed heater use during the first trimester of pregnancy. Compared with non-users, rates of spontaneous abortion were lower for women who used electric bed heaters. The adjusted odds ratio and 95% confidence interval (CI) for the two major devices used, electric blankets (N = 524) and waterbeds (N = 796), were, respectively, 0.8 (95% CI = 0.5-1.1) and 0.9 (95% CI = 0.7-1.2). An increase of risk with increasing intensity (setting-duration combination) of use was not observed. Users of electric blankets at low settings for most of the night (N = 171) had lower risks of spontaneous abortion than non-users (adjusted odds ratio = 0.5; 95% CI = 0.3-1.0). Twenty women who used electric blankets at a high setting for 1 hour or less had an adjusted odds ratio of 3.0 (95% CI = 1.1-8.3), but we found no spontaneous abortions among the few women (N = 13) who used a high setting for 2 or more hours. We found that exposure rankings of the magnetic field time-weighted average and a rate of change metric did not correspond monotonically to the pattern of spontaneous abortion risks and that electric blankets contribute less to overnight time-weighted average magnetic fields than has been thought.

ATP release by mechanically loaded porcine chondrons in pellet culture

OBJECTIVE

To determine whether ATP is released from chondrocytes during mechanical stimulation and whether degradation of ATP generates inorganic pyrophosphate in chondron pellet cultures.

METHODS

Chondron pellets were formed from 1.6 x 10(6) cells that had been enzymatically isolated from porcine articular cartilage. ATP was measured in media from cultures at rest and during fluid movement and cyclic compression. ATP hydrolysis was examined by high-performance liquid chromatography following the addition of gamma32P-ATP to resting cultures.

RESULTS

Pellet cultures at rest maintained a steady-state concentration of 2-4 nM ATP in 2 ml of medium. The ATP concentration increased 5-12-fold with cyclic compression (7.5 and 15 kPa at 0.5 Hz), then decreased to preloading levels within 60 minutes despite continued loading. A subsequent increase in pressure stimulated a further increase in ATP release, suggesting that chondrocytes desensitize to load. Cell viability was similar for pellets at rest and up to 24 hours after compression. ATP released in response to mechanical stimulation was inhibited 50% by 0.5 mM octanol, suggesting a regulated mechanism for ATP release. Exogenous ATP was rapidly hydrolyzed to pyrophosphate in resting cultures.

CONCLUSION

The occurrence of basal levels of extracellular ATP in the presence of pyrophosphohydrolase activity indicates that ATP was continuously released by chondrocytes at rest. Considering that chondrocytes express purinoceptors that respond to ATP, we suggest a role for ATP in extracellular signaling by chondrocytes in response to mechanical load. ATP released by chondrocytes in response to mechanical load is a likely source of pyrophosphate in calcium pyrophosphate dihydrate crystal deposition diseases.

Intercellular adhesion can be visualized using fluorescently labeled fibrosarcoma HT1080 cells cocultured with hematopoietic cell lines or CD34(+) enriched human mobilized peripheral blood cells

BACKGROUND

Intercellular contacts between adjacent cells migrating over each other are important in many cellular processes. However, it has been difficult to visualize and identify dynamic intercellular adhesions between migrating cells in situ.

METHODS

Two fluorescent membrane dyes, PKH2 and PKH26 for staining HT1080 and hematopoietic cells and cell lines, and an automated fluorescence microscopy system were used to monitor intercellular adhesion.

RESULTS

Cellular extensions connecting two or more adjacent cells were visualized, showing the intercellular adhesion between migrating cells for minutes and up to hours. After cells adhered to each other, followed by cell migration in different directions, cellular extensions were dragged from the pivotal contact points in different focal planes. CD34(+)-enriched mobilized peripheral blood cells and six hematopoietic cell lines showed intercellular connections in cocultures with HT1080. However, the frequency of intercellular connections was variable in different cocultures. A cell density of about 3.1 x 10(4) cells/cm(2) for both cell lines in cocultures provided an adequate number of cells in each field of view, showing up to four intercellular connections per 100 total cells plated.

DISCUSSION

The tools derived from this study will open new areas of investigation for understanding the mechanism of the intercellular adhesion process.

Extension of osmolality-induced podia is observed from fluorescently labeled hematopoietic cell lines in hyperosmotic medium

BACKGROUND

Since the description of long podia extended by hematopoietic cells and cell lines, the reliable elicitation of podia extensions is needed to study these podia systemically. In this study, hyperosmotic stress was considered as an elicitor.

METHODS

Using two fluorescent membrane dyes PKH2 and PKH26, and an automated fluorescence microscopy system, morphological changes of seven human cell lines (six hematopoietic, one fibrosarcoma) at different osmolalities were monitored. Presence of surface molecules on the hyperosmolality-induced podia (osmopodia) was examined.

RESULTS

In hyperosmotic medium, cells shrank rapidly, followed by osmopodia extension. Cells exhibited variable number (up to five) and length (up to longer than 100 microm) of osmopodia in about 1 h. Dead cells did not extend podia. Frequency, length, and number of podia were variable among cell lines studied. CD44 and CD45 were not present on the osmopodia, although they were present on the cell surface, showing that osmopodia characteristics differ from the podia observed previously in isotonic media. The osmopodia extension process was shown to be reversible upon repeated osmolality changes.

CONCLUSIONS

Osmopodia extended by human hematopoietic cell lines display a newly observed cellular morphology and provide a tool for investigation of dynamic cellular response to environmental changes.

Hyperosmotic pressure enhances immunoglobulin transcription rates and secretion rates of KR12H-2 transfectoma

When subjected to hyperosmotic pressure resulting from NaCl addition, KR12H-2 transfectoma, like most hybridomas, displayed a decrease in specific growth rate (mu) and an increase in specific antibody productivity (q(Ab)). Elevation of medium osmolality from 285 to 425 mOsm/kg decreased mu by 20%, while it increased q(Ab) by 376%. Although cell mass also increased at higher osmolality, it was not the main factor in increasing q(Ab). Hyperosmotic pressure was found to enhance transcription levels of immunoglobulin (Ig) mRNAs preferentially, compared with non-IgG mRNA. The transcription levels of both heavy chain (HC) and light chain (LC) mRNAs were enhanced as much as q(Ab). This result suggests that enhanced q(Ab) at higher osmolality was mainly due to enhanced transcription levels of Ig mRNA. However, these increased transcription levels of Ig mRNAs were not due to the enhanced stability of Ig mRNA. In fact, the stability of Ig mRNAs decreased at higher osmolality. Elevation of osmolality from 285 mOsm/kg to 425 mOsm/kg decreased the half-lives of HC and LC mRNAs by 37% and 36%, respectively. A simple mathematical model revealed that transcription rates of Ig mRNAs increased by more than 476% at 425 mOsm/kg. These elevated transcription levels could, in turn, increase the translation rates of Ig polypeptides. However, the translation rates of Ig polypeptides were not enhanced as much as the transcription levels of Ig mRNAs and q(Ab). The elevation of osmolality from 285 mOsm/kg to 425 mOsm/kg increased HC and LC mRNA specific translation rates by 172% and 240%, respectively. Taken together, the data suggest that (1) enhanced q(Ab) of KR12H-2 transfectoma at higher osmolality is due to elevated transcription rates of Ig mRNAs and expedited post-translational processing of Ig, and (2) antibody secretion by KR12H-2 transfectoma is most likely controlled at the level of Ig translation, particularly HC translation.

The incidence of enlarged chondrons in normal and osteoarthritic human cartilage and their relative matrix density

OBJECTIVE

To quantitate changes in the pericellular matrix in osteoarthritic (OA) articular cartilage.

DESIGN

Chondrons were enzymatically isolated from normal and OA human cartilage. The cross-sectional area of the chondrons were measured. After immunolabeling for keratan sulfate, type VI collagen and type II collagen, the relative matrix density was determined for different size classes of chondrons with quantitative fluorescence microscopy.

RESULTS

For individual chondrons, the average cross-sectional area (344+/-28 microm(2), mean+/-SE) for the normal specimens was significantly smaller than the average area (439+/-30 microm(2)) for the OA specimens. Using 496 microm(2) (mean+2 SD of the normal area) as the cut-off for enlarged chondrons, 33% of individual OA chondrons were enlarged compared to 16% for the normal. Chondrons under 300 microm(2) had a significantly higher density of keratan sulfate and type VI collagen than larger chondrons, while chondrons over 400 microm(2) had similar matrix densities.

CONCLUSIONS

There is a higher incidence of enlarged chondrons in OA cartilage than in normal cartilage. The enlargement may initially be due to hydrodynamic swelling but further increases in size are due to increased matrix deposition.

Cytogenetic analysis of chimeric antibody-producing CHO cells in the course of dihydrofolate reductase-mediated gene amplification and their stability in the absence of selective pressure

Previously, the highest producing (HP) recombinant CHO subclones isolated at various methotrexate (MTX) levels showed different antibody production stability during long-term culture, although they were clonally derived from CS13 transformant. In this study, genetic basis for their difference in antibody production stability was investigated using southern blot hybridization and fluorescence in situ hybridization (FISH) techniques. Southern analysis of HP subclones revealed that light-chain (LC) and heavy-chain (HC) cDNAs were located closely within 23 kb on an amplification unit, and the configuration of LC and HC cDNAs within this amplification unit was not disrupted during long-term culture in the absence of MTX. However, when LC and HC genes were localized on the metaphase chromosomes of HP subclones using FISH, the amplified sequences were present as an extended array on diverse marker chromosomes. HP subclones selected at higher MTX level had more kinds of marker chromosomes. CS13*-002 isolated at 0.02 microM MTX had only one marker chromosome (m002), whereas CS13*-1.0 isolated at 1 microM MTX had five different ones (m10A, m10B, m10C, m10D, and m10E). Each marker chromosome showed different fate during long-term culture of HP subclones in the absence of MTX, resulting in different degrees of stability among the HP subclones. The m10A and m10B remained unchanged, whereas the others disappeared or evolved to variants with shortened amplified arrays. The cells containing stable marker chromosomes constituted dominant subpopulations in CS13*-1.0, and thereby CS13*-1.0 became most stable in regard to antibody production during long-term culture. Furthermore, our dual-color FISH showed that the telomeric ends of amplified arrays on the stable marker chromosomes were always surrounded by (TTAGGG)(n) sequences, indicating that (TTAGGG)(n) sequences are closely related to the stability and evolution of amplified sequences. Taken together, our data show that the assessment of genotypic stability of amplified CHO cells is a prerequisite for understanding their production stability during long-term culture in the absence of selection pressure.

Phototoxicity of the fluorescent membrane dyes PKH2 and PKH26 on the human hematopoietic KG1a progenitor cell line

BACKGROUND

The phototoxic effects of the well-known fluorescent membrane dyes PKH2 and PKH26 have been unknown, although their use in cell tracking experiments has increased dramatically. To eliminate the phototoxicity-induced alteration in cell function and morphology, it is essential to examine the suspicious phototoxicity of these dyes.

METHODS

Chemical and phototoxic effects of PKH dyes on the human hematopoietic KG1a cell line were examined. To minimize phototoxicity in long-term cell tracking experiments lasting up to 18 h with a fluorescence microscope system, time-lapse monitoring with different time intervals and exposure times was introduced.

RESULTS

There were no significant effects of the two PKH dyes on cell viability and growth when using dye concentrations up to 5 microM. However, when stained cells were exposed to excitation light, cell viability decreased dramatically, showing the phototoxicity of the PKH dyes. More than 60% of cells stained with 5 microM PKH26 died after 5 min of continuous light exposure. The phototoxic effect was more extensive in cells stained with higher concentrations of the dyes.

CONCLUSIONS

We present guidelines for the optimal use of these dyes by using a defined hardware configuration.

Cancer in California school employees, 1988-1992

BACKGROUND

Periodic concerns about excesses of cancer among teachers in California schools prompted our examination of cancer incidence in California school employees.

METHODS

Records of school employees between 1987-1992 were linked to the California Cancer Registry of incident cases diagnosed 1988-1992. Sex-, race-, and age-adjusted standardized incidence ratios were calculated for specific cancer sites. Analyses stratified by sex, race/ethnicity, and job assignment were also performed.

RESULTS

Melanoma of the skin, thyroid cancer, prostate cancer, and female cancers of the breast, uterus, and ovary all occurred more frequently than expected in these school employees. In contrast, cancers of the respiratory system, oral cavity, digestive system, urinary system, and uterine cervix occurred less frequently.

CONCLUSIONS

The incidence of cancers thought to be related to hormones and/or higher socioeconomic status appeared elevated while cancers often linked to smoking and/or alcohol intake occurred less frequently in this large cohort of professional school employees.

Phototoxicity of the fluorescent membrane dyes PKH2 and PKH26 on the human hematopoietic KG1a progenitor cell line

BACKGROUND

The phototoxic effects of the well-known fluorescent membrane dyes PKH2 and PKH26 have been unknown, although their use in cell tracking experiments has increased dramatically. To eliminate the phototoxicity-induced alteration in cell function and morphology, it is essential to examine the suspicious phototoxicity of these dyes.

METHODS

Chemical and phototoxic effects of PKH dyes on the human hematopoietic KG1a cell line were examined. To minimize phototoxicity in long-term cell tracking experiments lasting up to 18 h with a fluorescence microscope system, time-lapse monitoring with different time intervals and exposure times was introduced.

RESULTS

There were no significant effects of the two PKH dyes on cell viability and growth when using dye concentrations up to 5 microM. However, when stained cells were exposed to excitation light, cell viability decreased dramatically, showing the phototoxicity of the PKH dyes. More than 60% of cells stained with 5 microM PKH26 died after 5 min of continuous light exposure. The phototoxic effect was more extensive in cells stained with higher concentrations of the dyes.

CONCLUSIONS

We present guidelines for the optimal use of these dyes by using a defined hardware configuration.

Development of a serum-free medium for the production of erythropoietin by suspension culture of recombinant Chinese hamster ovary cells using a statistical design

In order to develop a serum-free (SF) medium for the production of erythropoietin (EPO) by suspension culture of recombinant Chinese hamster ovary (rCHO) cells, a statistical optimization approach based on a Plackett-Burman design was adopted. A basal medium was prepared by supplementing Iscove's modified Dulbecco's medium (IMDM) with Fe(NO3)3.9H2O, CuCl2 and ZnSO4.7H2O which are generally contained in SF medium formulations. Insulin, transferrin and ethanolamine were also supplemented to the basal medium to determine their optimal concentrations. From this statistical analysis, glutamate, serine, methionine, phosphatidylcholine, hydrocortisone and pluronic F68 were identified as positive determinants for cell growth. The SF medium was formulated by supplementing the basal medium with components showing positive effects on cell growth in suspension culture. An EPO titer in this optimized SF medium was 79% of that in IMDM supplemented with 5% dialyzed fetal bovine serum (dFBS). Furthermore, the in vitro and in vivo biological activities of EPO produced in the SF medium were comparable to those produced in the serum-supplemented medium. Taken together, the results obtained here show that a Plackett-Burman design facilitates the development of SF media for the production of EPO by suspension culture of rCHO cells.

Cell surface receptors transmit sufficient force to bend collagen fibrils

To better understand the dynamic interaction of cells with their surrounding extracellular matrix, chondrocytes and rat embryo fibroblasts were overlaid with individual collagen fibrils and observed with high-resolution video-enhanced differential interference contrast microscopy. Although the cells had a polygonal shape characteristic of nonmotile cells, they used processes usually associated with cell locomotion to acquire the collagen fibrils. Instead of being transported in a retrograde direction, fibrils on the dorsal cell surface were bent, and regions of the bent fibrils were shifted in diverse directions. A blocking antibody to the beta1 integrin subunit significantly inhibited collagen fibril acquisition and bending. Enhanced actin assembly was only occasionally associated with fibrils undergoing rearrangement. Considering that the relatively stiff collagen fibrils require the application of force to be bent, this study shows that cells with a polygonal morphology (as opposed to a polarized, motile shape) are capable of exerting force through the beta1 integrins on the dorsal surface of the cell. Analysis of the bending patterns indicates that fibril buckling was induced by retrograde force combined with regions held stationary and/or the fibrils were bent by forces acting in opposing directions.

Development of a serum-free medium for dihydrofolate reductase-deficient Chinese hamster ovary cells (DG44) using a statistical design: beneficial effect of weaning of cells

To develop serum-free (SF) medium for dihydrofolate reductase-deficient Chinese hamster ovary cells (DG44), a statistical optimization approach based on a Plackett-Burman design was adopted. DG44 cells which were normally maintained in 10 serum medium were gradually weaned to 0.5% serum medium to increase the probability of successful growth in SF medium. A basal medium was prepared by supplementing Dulbecco's modified Eagle's medium and Ham's nutrient mixture F12 with hypoxanthine (10 mg/l) and thymidine (10 mg/l). Twenty-eight different supplements were selected as variables on the basis of their growth-promoting abilities. From statistical analysis, leucine, tryptophan, lysine, proline, histidine, hydrocortisone, ethanolamine, and phosphatidylcholine were identified as important components showing positive effects on cell growth. A new SF medium (SF-DG44) was formulated by supplementing the basal medium with these components. When the weaned cells were inoculated at 1.0 x 10(5) cells/ml, a maximum viable cell concentration of 6.4 x 10(3)) cells/ ml was achieved in SF-DG44 medium. In contrast, when the unweaned cells were used, a concentration of only 4.1 x 10(5) cells/ml was reached under the same culture conditions, indicating that weaning of cells improves cell growth in SF medium. In summary, we found that development of a novel SF medium for DG44 cells was facilitated using a Plackett-Burman design technique and weaning of cells.

Alterations in the Young's modulus and volumetric properties of chondrocytes isolated from normal and osteoarthritic human cartilage

The mechanical environment of the chondrocyte is an important factor that influences the maintenance of the articular cartilage extracellular matrix. Previous studies have utilized theoretical models of chondrocytes within articular cartilage to predict the stress-strain and fluid flow environments around the cell, but little is currently known regarding the cellular properties which are required for implementation of these models. The objectives of this study were to characterize the mechanical behavior of primary human chondrocytes and to determine the Young's modulus of chondrocytes from non-osteoarthritic ('normal') and osteoarthritic cartilage. A second goal was to quantify changes in the volume of isolated chondrocytes in response to mechanical deformation. The micropipette aspiration technique was used to measure the deformation of a single chondrocyte into a glass micropipette in response to a prescribed pressure. The results of this study indicate that the human chondrocyte behaves as a viscoelastic solid. No differences were found between the Young's moduli of normal (0.65+/-0.63 kPa, n = 44) and osteoarthritic chondrocytes (0.67+/-0.86 kPa, n = 69, p = 0.93). A significant difference in cell volume was observed immediately and 600 s after complete aspiration of the cell into the pipette (p < 0.001), and the magnitude of this volume change between normal (11+/-11%, n = 40) and osteoarthritic (20+/-11%, n = 41) chondroctyes was significantly different at both time points (p < 0.002). This finding suggests that chondrocytes from osteoarthritic cartilage may have altered volume regulation capabilities in response to mechanical deformation. The mechanical and volumetric properties determined in this study will be of use in analytical and finite element models of chondrocyte-matrix interactions in order to better predict the mechanical environment of the cell in vivo.

Application of hypoosmolar medium to fed-batch culture of hybridoma cells for improvement of culture longevity

Cell culture longevity in fed-batch culture of hybridomas is often limited by elevated medium osmolality caused by repeated nutrient feeding. Shotwise feeding of 10x Dulbecco's modified Eagle's medium (DMEM) concentrates elevated the osmolality of medium up to 540 mOsm/kg at the end of fed-batch culture of S3H5/gamma2bA2 hybridoma which is known to be lethal to most hybridomas. S3H5/gamma2bA2 hybridoma has been shown to grow without significant growth depression at 219 mOsm/kg in DMEM supplemented with 10% fetal bovine serum. To improve culture longevity in fed-batch cultures of S3H5/gamma2bA2 hybridoma, a hypoosmolar medium (223 mOsm/kg) was used as an initial basal medium. The use of hypoosmolar medium delayed the onset of severe cell death resulting from elevated osmolality and allowed one more addition of 10x DMEM concentrates to the culture. As a result, a final antibody concentration obtained was 121.5 microg/mL which is approximately 1.5-fold higher compared to fed-batch culture using a standard medium (335 mOsm/kg). When compared to batch culture, a more than 5-fold increase in the final antibody concentration was achieved. Taken together, the use of hypoosmolar medium as an initial medium in fed-batch culture improved culture longevity of S3H5/gamma2bA2 hybridoma, resulting in a substantial increase in the final antibody concentration.

The deformation behavior and mechanical properties of chondrocytes in articular cartilage

INTRODUCTION

Chondrocytes in articular cartilage utilize mechanical signals to regulate their metabolic activity. A fundamental step in determining the role of various biophysical factors in this process is to characterize the local mechanical environment of the chondrocyte under physiological loading.

METHODS

A combined experimental and theoretical approach was used to quantify the in-situ mechanical environment of the chondrocyte. The mechanical properties of enzymatically-isolated chondrocytes and their pericellular matrix (PCM) were determined using micropipette aspiration. The values were used in a finite element model of the chondron (the chondrocyte and its PCM) within articular cartilage to predict the stress-strain and fluid flow microenvironment of the cell. The theoretical predictions were validated using three-dimensional confocal microscopy of chondrocyte deformation in situ.

RESULTS

Chondrocytes were found to behave as a viscoelastic solid material with a Young's modulus of approximately 0.6 kPa. The elastic modulus of the PCM was significantly higher than that of the chondrocyte, but several orders of magnitude lower than that of the extracellular matrix. Theoretical modeling of cell-matrix interactions suggests the mechanical environment of the chondrocyte is highly non-uniform and is dependent on the viscoelastic properties of the PCM. Excellent agreement was observed between the theoretical predictions and the direct measurements of chondrocyte deformation, but only if the model incorporated the PCM.

CONCLUSIONS

These findings imply that the PCM plays a functional biomechanical role in articular cartilage, and alterations in PCM properties with aging or disease will significantly affect the biophysical environment of the chondrocyte.

Clonal variability within dihydrofolate reductase-mediated gene amplified Chinese hamster ovary cells: stability in the absence of selective pressure

Recombinant Chinese hamster ovary (rCHO) cells expressing a high level of chimeric antibody were obtained by cotransfection of heavy- and light-chain cDNA expression vectors into dihydrofolate reductase-deficient CHO cells and subsequent gene amplification in medium containing stepwise increments in methotrexate (MTX) level up to 1.0 microM. To determine the clonal variability within the amplified cell population in regard to antibody production stability, 20 subclones were randomly isolated from the amplified cell population at 1.0 microM MTX (CS13-1.0 cells). Clonal analysis showed that CS13-1.0 cells were heterogeneous with regard to specific growth rate (mu) and specific antibody productivity (qAb), although they were derived from a single clone. The mu and qAb of 20 subclones were in the range of 0.51 to 0.72 day-1 and 10.9 to 19.1 microgram/10(6) cells/day, respectively. During 8 weeks of cultivation in the absence of selective pressure, the mu of most subclones did not change significantly. On the other hand, their qAb decreased significantly. Furthermore, the relative decrease in qAb varied among subclones, ranging from 30% to 80%. Southern and Northern blot analyses showed that this decreased qAb resulted mainly from the loss of amplified immunoglobulin (Ig) gene copies and their respective cytoplasmic mRNAs. For the sake of screening convenience, an attempted was made to correlate the initial properties of subclones (such as mu, qAb, and Ig gene copies) with their antibody production stability during long-term culture. Among these initial properties examined, only qAb of subclones could help to predict their stability to some extent. The subclones with high qAb were relatively stable with regard to antibody production during long-term culture in the absence of selective pressure (P < 0. 005, ANOVA). Taken together, the clonal heterogeneity in an amplified CHO cell population necessitates clonal analysis for screening stable clones with high qAb.

Development of a serum-free medium for the production of humanized antibody from Chinese hamster ovary cells using a statistical design

To develop serum-free (SF) media for the production of humanized antibody from recombinant Chinese hamster ovary (rCHO) cells, a statistical optimization approach based on a Plackett-Burman design was adopted. A basal medium was prepared by supplementing alpha-minimal essential medium (alpha-MEM) with Fe(NO3)3.9H2O, CuCl2, ZnSO4.7H2O, and Na2SeO3 which are generally contained in SF medium formulations. Insulin, transferrin, and ethanolamine were also supplemented to the basal medium to determine their optimal concentrations. From this statistical analysis, serine, phenylalanine, and tyrosine were identified as important determinants for cell growth. Also, putrescine, linoleic acid, and hydrocortisone were shown to be important for both cell growth and antibody production. The SF medium was formulated by supplementing the basal medium with components showing positive effects on cell growth and/or antibody production. Cell growth and antibody production in this SF medium were comparable to those in alpha-MEM supplemented with 5% dialyzed fetal bovine serum. Taken together, the results obtained here show that a Plackett-Burman design facilitates the development of SF media for rCHO cells aimed at producing a humanized antibody.

Risk of bacteremia for febrile young children in the post-Haemophilus influenzae type b era

OBJECTIVES

To determine the risk for bacteremia, in the post-Haemophilus influenzae type b era, in a prospective cohort of well-appearing febrile children 3 to 36 months of age with no obvious source of infection; and to compare the predictive abilities of objective criteria in identification of children with occult pneumococcal bacteremia from those at risk.

DESIGN

All children seen from 1993 through 1996, 3 to 36 months of age with a temperature of 39.0 degrees C or higher, no identified source of infection (except otitis media), and discharged to home were considered to be at risk for occult bacteremia and included in the study.

SETTING

Urban pediatric emergency department.

RESULTS

Of 199868 patient visits to the emergency department, 1911 children were considered to be at risk for occult bacteremia. Blood cultures were obtained from 9465 (79%). A total of 149 blood cultures contained pathogenic organisms, indicating a rate of occult bacteremia of 1.57% (95% confidence intervals: 1.32%-1.83%). White blood cell count and absolute neutrophil count were the best predictors for occult pneumococcal bacteremia. Using a white blood cell count cutoff value of 15 cells x 10(9)/L (sensitivity, 86%; specificity, 77%; and positive predictive value, 5.1%) would result in the treatment of approximately 19 nonbacteremic children for each bacteremic child treated.

CONCLUSIONS

The prevalence of occult bacteremia in children 3 to 36 months old with temperatures of 39.0 degrees C or higher and no obvious source of infection is 1.6%. The white blood cell and absolute neutrophil counts are the most accurate predictors of occult pneumococcal bacteremia and when available should be used if presumptive antibiotic therapy is being considered.

Characterization of chimeric antibody producing CHO cells in the course of dihydrofolate reductase-mediated gene amplification and their stability in the absence of selective pressure

Recombinant Chinese hamster ovary (CHO) cells expressing a high-level of chimeric antibody against S surface antigen of hepatitis B virus were obtained by co-transfection of heavy and light chain cDNA expression vectors into dihydrofolate reductase (dhfr)-deficient CHO cells and subsequent gene amplification in medium containing stepwise increments in methotrexate (MTX) level such as 0.02, 0.08, 0.32, 1.0, and 4.0 microM. The highest producer (HP) subclone was isolated from each MTX level and was characterized with respect to cell growth and antibody production in the corresponding level of MTX. The specific growth rate of the HP subclone was inversely proportional to the MTX level. On the other hand, its specific antibody productivity (qAb) rapidly increased with increasing MTX level up to 0.08 microM, and thereafter, it gradually increased to 20 microg/10(6) cells/day at 4 microM MTX. Southern blot analysis showed that the enhanced qAb at higher MTX level resulted from immunoglobulin (Ig) gene amplification. The stability of the HP subclones isolated at 0.02, 0.08, 0.32, and 1.0 microM MTX in regard to antibody production was investigated during long-term culture in the absence of MTX. The qAb of all subclones significantly decreased during the culture. However, the relative extent of decrease in qAb was variable among the subclones. The HP subclone isolated at 1 microM MTX was most stable and could retain 59% of the initial qAb after 80 days of cultivation. Southern blot analysis showed that this decrease in qAb of the subclones resulted mainly from the loss of Ig gene copies during long-term culture. Despite the decreased qAb, the HP subclone isolated at 1 microM MTX could maintain high volumetric antibody productivity over three months because of improved cell growth rate during long-term culture.

Activation of transgene expression by early region 4 is responsible for a high level of persistent transgene expression from adenovirus vectors in vivo

The persistence of transgene expression has become a hallmark for adenovirus vector evaluation in vivo. Although not all therapeutic benefit in gene therapy is reliant on long-term transgene expression, it is assumed that the treatment of chronic diseases will require significant persistence of expression. To understand the mechanisms involved in transgene persistence, a number of adenovirus vectors were evaluated in vivo in different strains of mice. Interestingly, the rate of vector genome clearance was not altered by the complete deletion of early region 4 (E4) in our vectors. The GV11 (E1- E4-) vector genome cleared with a similar kinetic profile as the GV10 (E1-) vector genome in immunocompetent and immunocompromised mice. These results suggest that the majority of adenovirus vector genomes are eliminated from transduced tissue via a mechanism(s) independent of T-cell, B-cell, and NK cell immune mechanisms. While the levels of persistence of transgene expression in liver or lung transduced with GV10 and GV11 vectors expressing beta-galactosidase, cystic fibrosis transmembrane conductance regulator, or secretory alkaline phosphatase were similar in immunocompetent mice, a marked difference was observed in immunocompromised animals. Levels of transgene expression initially from both GV10 and GV11 vectors were the same. However, GV11 transgene expression correlated with loss of vector genome, while GV10 transgene expression persisted at a high level. Coadministration and readministration of GV10 vectors showed that E4 provided in trans could activate transgene expression from the GV11 vector genome. While transgene expression activity per genome from the GV10 vector is clearly activated, expression from a cytomegalovirus promoter expression cassette in a GV11 vector appeared to be further inactivated as a function of time. Understanding the molecular mechanisms underlying these expression effects will be important for developing persistent adenovirus vectors for chronic applications.

Increased in vitro and in vivo gene transfer by adenovirus vectors containing chimeric fiber proteins

Alteration of the natural tropism of adenovirus (Ad) will permit gene transfer into specific cell types and thereby greatly broaden the scope of target diseases that can be treated by using Ad. We have constructed two Ad vectors which contain modifications to the Ad fiber coat protein that redirect virus binding to either alpha(v) integrin [AdZ.F(RGD)] or heparan sulfate [AdZ.F(pK7)] cellular receptors. These vectors were constructed by a novel method involving E4 rescue of an E4-deficient Ad with a transfer vector containing both the E4 region and the modified fiber gene. AdZ.F(RGD) increased gene delivery to endothelial and smooth muscle cells expressing alpha(v) integrins. Likewise, AdZ.F(pK7) increased transduction 5- to 500-fold in multiple cell types lacking high levels of Ad fiber receptor, including macrophage, endothelial, smooth muscle, fibroblast, and T cells. In addition, AdZ.F(pK7) significantly increased gene transfer in vivo to vascular smooth muscle cells of the porcine iliac artery following balloon angioplasty. These vectors may therefore be useful in gene therapy for vascular restenosis or for targeting endothelial cells in tumors. Although binding to the fiber receptor still occurs with these vectors, they demonstrate the feasibility of tissue-specific receptor targeting in cells which express low levels of Ad fiber receptor.

Transient confinement of a glycosylphosphatidylinositol-anchored protein in the plasma membrane

Glycosylphosphatidylinositol (GPI)-anchored proteins participate in many cell surface functions; however, the molecular associations of these lipid-linked proteins within the plasma membrane are not well understood. Recent biochemical analyses of detergent insoluble membrane fractions have suggested that GPI-anchored proteins may be associated with glycosphingolipid (GSL)-enriched domains that also contain cholesterol and signaling molecules such as Src family kinases and, in some cases, caveolae. The movements of two components of the putative GSL-enriched domains, Thy-1, a GPI-anchored protein, and GM1, a GSL, were followed with single particle tracking on C3H 10T1/2 cell surfaces and categorized into four modes of lateral transport, fast diffusion, slow anomalous diffusion, diffusion confined to 325-370 nm diameter regions, and a fraction of molecules that was essentially stationary on the 6.6 s time scale. Longer observations (60 s) showed that Thy-1 and GM1 are transiently confined for 7-9 s to regions averaging 260-330 nm in diameter. Approximately 35-37% of both Thy-1 and GM1 undergo confined diffusion, whereas only 16% of fluorescein phosphatidylethanolamine, a phospholipid analog which is not expected to be found in the GSL domains, experience confined diffusion to regions averaging approximately 230 nm in diameter. Further, when glycosphingolipid expression was reduced approximately 40% with the glucosylceramide synthase inhibitor, d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, the percentage of trajectories exhibiting confinement and the size of the confining domain for Thy-1 were reduced approximately 1.5-fold. In contrast, extraction of cells with Triton X-100 leaves the fraction of molecules confined and the domain sizes of Thy-1 and GM1 unchanged. Our results are consistent with the preferential association of GPI-anchored proteins with glycosphingolipid-enriched domains and suggest that the confining domains may be the in vivo equivalent of the detergent insoluble membrane fractions.

Targeted adenovirus-mediated gene delivery to T cells via CD3

T cells are primary targets in numerous gene therapy protocols. However, the use of subgroup C adenovirus serotype 2 or 5 (Ad2 or Ad5) as a vector to transduce T cells is limited by its poor transduction efficiency for these cells. In this report we show that poor T-cell transduction results from these cells lacking both the primary Ad2-Ad5 receptor, used in attachment, and the secondary Ad receptor, which mediates entry of most adenovirus serotypes. These deficiencies were overcome by using a bispecific antibody (bsAb) with specificities for human CD3 and for a FLAG epitope genetically introduced into Ad5 (Ad.FLAG) to redirect the virus to human T cells. The anti-FLAG x anti-CD3 bsAb increased Ad.FLAG binding 30-fold, induced the efficient uptake of Ad.FLAG into the cells, and led to a 100- to 500-fold increase in the transduction of resting T cells. Moreover, fluorescence-activated cell sorter analysis showed that 25 to 90% of the T cells were transduced by the bsAb-complexed Ad.FLAG at multiplicities of infection between 20 and 100 active particles per cell. These results demonstrate that bsAbs can target Ad to non-Ad receptors on cells that are normally resistant to Ad, resulting in their efficient and specific transduction.

Anaerobic and aerobic degradation of pyridine by a newly isolated denitrifying bacterium

New denitrifying bacteria that could degrade pyridine under both aerobic and anaerobic conditions were isolated from industrial wastewater. The successful enrichment and isolation of these strains required selenite as a trace element. These isolates appeared to be closely related to Azoarcus species according to the results of 16S rRNA sequence analysis. An isolated strain, pF6, metabolized pyridine through the same pathway under both aerobic and anaerobic conditions. Since pyridine induced NAD-linked glutarate-dialdehyde dehydrogenase and isocitratase activities, it is likely that the mechanism of pyridine degradation in strain pF6 involves N-C-2 ring cleavage. Strain pF6 could degrade pyridine in the presence of nitrate, nitrite, and nitrous oxide as electron acceptors. In a batch culture with 6 mM nitrate, degradation of pyridine and denitrification were not sensitively affected by the redox potential, which gradually decreased from 150 to -200 mV. In a batch culture with the nitrate concentration higher than 6 mM, nitrite transiently accumulated during denitrification significantly inhibited cell growth and pyridine degradation. Growth yield on pyridine decreased slightly under denitrifying conditions from that under aerobic conditions. Furthermore, when the pyridine concentration used was above 12 mM, the specific growth rate under denitrifying conditions was higher than that under aerobic conditions. Considering these characteristics, a newly isolated denitrifying bacterium, strain pF6, has advantages over strictly aerobic bacteria in field applications.