Diversity and critical behavior in prisoner's dilemma game.

The prisoner's dilemma (PD) game is a simple model for understanding cooperative patterns in complex systems. Here, we study a PD game problem in scale-free networks containing hierarchically organized modules and controllable shortcuts connecting separated hubs. We find that cooperator clusters exhibit a percolation transition in the parameter space (p,b), where p is the occupation probability of shortcuts and b is the temptation payoff in the PD game. The cluster size distribution follows a power law at the transition point. Such a critical behavior, resulting from the combined effect of stochastic processes in the PD game and the heterogeneity of complex network structure, illustrates diversities arising in social relationships and in forming cooperator groups in real-world systems.

Spectral dimensions of hierarchical scale-free networks with weighted shortcuts.

Spectral dimensions have been widely used to understand transport properties on regular and fractal lattices. However, they have received little attention with regard to complex networks such as scale-free and small-world networks. Here, we study the spectral dimension and the return-to-origin probability of random walks on hierarchical scale-free networks, which can be either fractal or nonfractal depending on the weight of the shortcuts. Applying the renormalization-group (RG) approach to a Gaussian model, we obtain the exact spectral dimension. While the spectral dimension varies between 1 and 2 for the fractal case, it remains at 2, independent of the variation in the network structure, for the nonfractal case. The crossover behavior between the two cases is studied by carrying out the RG flow analysis. The analytical results are confirmed by simulation results and their implications for the architecture of complex systems are discussed.

Is Pneumocystis carinii vertically transmitted to neonatal rats?

Pneumocystis carinii is a pulmonary pathogen of immunocompromised humans or other mammals. Its infection results from activation of organisms involved in latent infection or from new infection through the air. Almost all children are known to be infected within 2 to 4 years of birth, though prenatal transplacental transmission has not yet been demonstrated. In this study we observed experimental P. carinii infection in neonatal rats, thus investigating the possibility of transplacental vertical transmission by Diff-Quik staining of the lung impression smears and in-situ hybridization for lung sections. The positive rate of P. carinii infection in immunosuppressed maternal rats was 100%, but that in normal maternal rats was 0%. Cystic forms of P. carinii were observed in three of six 1-week old neonatal rats born of heavily infected mothers, but none of them was positive by in-situ hybridization. Five weeks after birth, cystic forms were detected in four neonatal rats. In the lobes of the lungs, no predilection site of P. carinii was recognized. Counts of cystic forms on smears and the reactivity of in-situ hybridization in the lungs of neonatal rats were significantly lower than in maternal rats. The present findings suggest that P. carinii is rarely transmitted through the placenta and proliferates less successfully in the lungs of neonatal rats than in mothers.

Role of intraepithelial lymphocytes in mucosal immune responses of mice experimentally infected with Cryptosporidium parvum.

In order to investigate the role of intestinal intraepithelial lymphocytes (IELs) in host defense against Cryptosporidium parvum infection, conventionally bred immunocompetent (ImCT) ICR mice and immunosuppressed (ImSP) littermates were infected orally with 10(6) C. parvum oocysts. Then fecal oocyst excretion, the number and location of IELs, and their T lymphocyte subsets were observed on days 4, 7, 10, 13, 16, and 20 postinfection (PI). Uninfected ImCT and ImSP mice were used as controls. The starting point of oocyst excretion was day 4 PI in both ImCT- and ImSP-infected mice. The highest oocyst excretion occurred on day 7 PI in both groups, though the number of oocysts excreted was 3 times greater in ImSP than in ImCT mice. In ImCT mice, IELs greatly increased in number on days 16 and 20 PI (P < 0.05), but the increase was minimal in ImSP mice. IELs changed their location from the basal area to intermediate and apical areas of villous epithelial cells during the early stage of infection. In ImCT-infected mice, IEL phenotypes also changed; whereas CD4+ cells increased temporarily on day 7 PI (P < 0.05), CD8+ cells increased significantly on days 16 and 20 PI (P < 0.05). The results strongly suggest that IELs play a significant role in host defense against C. parvum infection, with helper T cells initiating control of the infection and cytotoxic T cells eliminating the parasites.

Toxoplasma gondii antibody titers in sera of children admitted to the Seoul National University Children's Hospital.

A total of 542 children under 10 years of age, admitted to the Seoul National University Children's Hospital, was examined for antibody titers of Toxoplasma gondii using indirect latex agglutination (ILA) test. Among them, 7.7% showed positive titers higher than 1:32, without significant difference between males (7.3%) and females (8.5%). The seropositive rate increased with age although the statistical significance was negligible (0.05 < P < 0.1). By residential areas, the prevalence appeared higher among children from southern provinces (Kyongsang-do and Cholla do) than those from other areas, but the statistical significance was also very low (0.05 < P < 0.1). When the seropositive cases were analyzed by coincidental diseases, the prevalence was significantly higher in patients with congenital diseases than in patients with non-congenital diseases (P < 0.05). The results showed that the seropositive rate of toxoplasmosis in children examined was not high compared with other endemic countries. Some correlations are suggested between toxoplasmosis and congenital anomalies in Korea.

Control of clonorchiasis by repeated praziquantel treatment and low diagnostic efficacy of sonography.

In Korea, Clonorchis sinensis infection is still highly prevalent because case detection in the field is difficult and the detected cases used to be incompletely cured due to treatment failure. The present study tried to control clonorchiasis in an endemic village by repeated treatments with praziquantel every 6 months and to evaluate sonography as a diagnostic measure. By stool examinations, the egg positive rate in the endemic village was 22.7%, but it decreased to 19.6% at 6 months, 15.1% at 12 months. 12.2% at 18 months, 6.3% at 24 months, 11.4% at 30 months, and 6.3% at 42 months after the beginning of repeated praziquantel administration. The sonography showed 61 (49.6%) positive cases of 123 screened residents: among egg-positives the sonography positive rate was 52.2% and among egg-negatives it was still 49%. The rate among cured cases was 64.3% after 6 months, 50.0% after 12 months, 50.0% after 18 months, and 66.7% after 24 months. In a non-endemic village, 64 residents were found egg-negative by fecal examination, but 20 (31.3%) of them were positive by sonography. The present findings indicate that control of clonorchiasis in an endemic village by repeated praziquantel treatment for 42 months is still insufficient and sonography is of little value for diagnosis of clonorchiasis.

Development of jaundice in Korean neonates after cesarean section.

The aim of the project was to determine the physiologic mechanisms of later- and higher-peak transitional plasma bilirubin levels in Korean infants. Blood carboxyhemoglobin, corrected for inhaled CO (COHbc), as an index of bilirubin production, and plasma total bilirubin levels in 40 healthy term Korean infants delivered by Cesarean section were measured throughout the first week of life. The COHbc levels were significantly higher in the Korean neonates than in previously studied Caucasian neonates. Moreover, COHbc levels decreased by 28% during the first 7 days of life from 0.85 +/- 0.20 to 0.61 +/- 0.34% (P < 0.025). This pattern parallels a 15% decrease in total hemoglobin from 181 +/- 23 to 154 +/- 53 g/L (P < 0.05). In contrast, plasma bilirubin concentrations more than doubled from 80 +/- 32 to 172 +/- 48 mumol/L (4.7 +/- 1.8 to 10.0 +/- 2.8 mg/dL; P < 0.001), remaining unchanged between days 4 and 7. Both increased production and decreased elimination of bilirubin contribute to physiologic jaundice in Korean infants.

Experimental infection of murine splenic lymphocytes and granulocytes with Toxoplasma gondii RH tachyzoites.

Toxoplasma gondii, an intracellular protozoan infecting many kinds of eukaryotic cells, has been used to experimentally infect macrophages, epithelial cells, fibroblasts, and various cancer cells, but rarely T and B lymphocytes or granulocytes. The present study was performed to determine the susceptibility of murine (BALB/c or CBA) splenic T and B lymphocytes, and granulocytes to infection with T. gondii RH tachyzoites. The ultrastructure of the infected host cells was observed by TEM, and the degree of intracellular parasite proliferation was quantified using 3H-uracil uptake assay. At 24 hrs post-culture, the host cell cytoplasm was found to contain 1 or 2, or a maximum of 7-8 tachyzoites. Infected T lymphocytes demonstrated a peripherally displaced nucleus, a parasitophorous vacuole enveloping the parasite, and an increased number of mitochondria. In B lymphocytes infected with tachyzoites, RER was not well developed compared to uninfected B lymphocytes. Uninfected granulocytes contained many electron-dense granules, but T. gondii-infected granulocytes demonstrated a decreased number of granules. Based on the 3H-uracil uptake assay, the susceptibility of T and B lymphocytes, and granulocytes, to infection with T. gondii tachyzoites was fairly high irrespective of cell type and strain of mouse. This strongly suggests deterioration in the functioning of infected host immune cells.

Viral etiology and epidemiology of acute lower respiratory tract infections in Korean children.

Viral etiologic agents of acute lower respiratory tract infections were studied from November, 1990, through April, 1994, in Korean children. From 712 children who visited or were admitted to Seoul National University Children's Hospital because of acute lower respiratory tract infections, 804 nasal aspirates were collected; viral agents were detected by virus isolation and virus antigen was detected by indirect immunofluorescent staining. One or more viral agents were identified in 369 (45.9%) cases; of which 3.3% were mixed infections. The pathogens identified were respiratory syncytial virus (27.2%), parainfluenza virus type 3 (7.8%), influenza A virus (3.9%), adenovirus (3.9%), parainfluenza virus type 1 (1.7%), influenza B virus (1.4%), parainfluenza virus type 2 (0.5%), measles virus (0.1%) and others (0.9%). The clinical patterns of viral lower respiratory tract included pneumonia (56.6%), bronchiolitis (35.2%), croup (6.5%) and tracheo-bronchitis (1.6%). Infections with respiratory syncytial virus, parainfluenza virus types 1 and 3 and influenza A and B virus occurred in epidemics, whereas adenovirus was isolated sporadically throughout the study period. The data expand our understanding of the epidemiology of acute viral lower respiratory tract infections in Korean children and may be helpful to the clinicians and researchers interested in the control of viral respiratory tract infections.

An immunohistochemical analysis of mdr-1 and bcl-2 expressions in neuroblastoma.

Among the differentiation-related changes in neuroblastoma are expressions of mdr-1 and bcl-2, which may be potentially related to the resistance to anticancer chemotherapy. In the present study, the authors performed an immunohistochemical analysis of mdr-1 and bcl-2 expressions in 30 neuroblastomas using monoclonal anti-P-glycoprotein(mdr-1 product) antibody and monoclonal anti-bcl-2 antibody to investigate the significance of their expression. The overall incidence of mdr-1 and bcl-2 expressions were 53.3% (16/30) and 93.3% (28/30), respectively. The expressions of mdr-1 and bcl-2 didn't seem to be related to the status of preoperative chemotherapy or stage of disease. The expression of mdr-1 was closely related to the differentiation of tumor cells (p < 0.01), especially to the neuronal differentiation. The bcl-2 expression was so common that it seemed to be indigenous to this neoplasm. The overall findings suggested that the expression of mdr-1 is one of the differentiation markers, while bcl-2 expression may partly explain the reasons for the relatively poor prognosis of neuroblastoma by the resistance to anticancer chemotherapy, which is a major therapeutic tool for this peculiar neoplasm.

Effects of gamma-irradiation on intracellular proliferation of Toxoplasma gondii RH tachyzoites.

A quantitative assay was performed on the effects of gamma-irradiation (30-300 Gy) on intracellular proliferation of Toxoplasma gondii RH tachyzoites in human leukemic HL-60 cells and murine peritoneal macrophages by means of 3H-uracil uptake assay. Infected non-irradiation group (NI) and uninfected group (incubating only host cells) were prepared. The 3H-uracil uptake by tachyzoites of NI group 12-24 hrs after infection was 2,190-4,787 counts per minute for macrophages and 2,967-8,254 for HL-60 cells, whereas the irradiated tachyzoites revealed only 381-703 (100 Gy) and 218-408 (300 Gy) for macrophages, and 1,911-2,618 (30 Gy), 1,253-1,384 (70 Gy), 1,013-1,090 (100 Gy), and 483-588 (300 Gy) for HL-60 cells. The proliferation inhibition rate was similar in macrophages and HL-60 cells, for example, 89-94% and 80-94% respectively by 300 Gy, 12-24 hrs after infection. It is concluded that RH tachyzoites of T. gondii are severely affected by gamma-irradiation in their capability of intracellular proliferation.

Karyotypes of Pneumocystis carinii from Korean rats.

Molecular karyotyping was applied to Pneumocystis carinii(Pc) from two strains of experimental rats, Sprague Dawley(SD) and Fisher(F), in Korea. Field inversion gel electrophoresis and contour clamped homogeneous electric field electrophoresis resolved 15 chromosomal bands from the Pc. The size of the bands was estimated 270kb to 684kb from SD rats, and 273kb to 713 kb from F rats. The bands of 283 kb from SD rats and of 273 kb from F rats stained more brightly suggesting duplicated bands. Total number of chromosomes was at least 16, and total genomic size was estimated 7 x 10(6) bp. All of the bands from F rats hybridized to the probe of repeated DNA sequences of Pc and the band of 448 kb size was proved to contain rDNA sequences, but Pc. chromosome bands from SD rats showed no reactions to the probes. The 2 different karyotypes of P. carinii from 2 strains of rats were maintained consistently for 2 years.

[Experimental activation of cryptosporidiosis in mice by immunosuppression].

Cryptosporidium, a coccidian parasite first described by Tyzzer (1907) from a laboratory mouse, has become an important human enteric pathogen causing overwhelming diarrhea especially in immunocompromised patients such as AIDS. This parasite has been reported from over 20 countries and is recognized as a cosmopolitan species. In Korea, however, there has been no report on human as well as animal cryptosporidiosis. This study was performed so as to verify the presence of Cryptosporidium in Korea by activating the parasite from laboratory mice by immunosuppression. Total 65 conventionally-bred ICR mice including a control (5 mice) and 3 experimental groups (20 each) were used for this study. Group I was immunosuppressed with prednisolone injection (1 mg IM, every other day) for 7 weeks. Group II (prednisolone injection and tetracycline administration) and Group III (prednisolone injection and trimethoprim-sulfamethoxazole administration) were prepared to observe the effect of antibacterial agents on the activation of cryptosporidiosis. In fecal examinations of mice Cryptosporidium oocysts (4-6 microns in size) were detected from 1 week after the start of immunosuppression and the mice began to die. In H-E stained tissue sections of the lower jejunum, numerous very small (2-4 microns), dense, ovoid or spherical, slightly basophilic bodies were seen attached on the free border of mucosal epithelial cells. In scanning and transmission electron microscopic observations, these organisms were identified as various developmental stages of Cryptosporidium. The species is considered to be C. parvum.(ABSTRACT TRUNCATED AT 250 WORDS)

[Development of Eimeria tenella in MDBK cell culture with a note on enhancing effect of preincubation with chicken spleen cells].

Eimeria tenella, an intracellular protozoan parasite infecting the epithelial cells of the ceca of chickens, causes severe diarrhea and bleeding that can lead its host to death. It is of interest that E. tenella first penetrate into the mucosal intraepithelial lymphocytes (IEL) before they parasitize crypt or villous epithelial cells. This in vitro study was undertaken to know whether the penetration of E. tenella into such a lymphoid cell is a beneficial step for the parasite survival and development. Three sequential experiments were performed. First, the in vitro established bovine kidney cell line, MDBK cells, were evaluated for use as host cells for E. tenella, through morphological observation. Second, the degree of parasite development and multiplication in MDBK cells was quantitatively assayed using radioisotope-labelled uracil (3H-uracil). Third, the E. tenella sporozoites viability was assayed after preincubation of them with chicken spleen cells. E. tenella oöcysts obtained from the ceca of the infected chickens were used for the source of the sporozoites. Spleen cells (E) obtained from normal chickens (FP strain) were preincubated with the sporozoites (T) at the E:T ratio of 100:1, 50:1 or 25:1 for 4 or 12 hours, and then the mixture was inoculated into the MDBK cell monolayer. Morphologically the infected MDBK cells revealed active schizogonic cycle of E. tenella in 3-4 days, which was characterized by the appearance of trophozoites, and immature and mature schizonts containing merozoites. The 3H-uracil uptake by E. tenella increased gradually in the MDBK cells, which made a plateau after 48-60 hours, and decreased thereafter. The uptake amount of 3H-uracil depended not only upon the inoculum size of the sporozoites but also on the degree of time delay (preincubation; sporozoites only) from excystation to inoculation into MDBK cells. The 3H-uracil uptake became lower as the preincubation time was prolonged. In comparison, after preincubation of sporozoites with spleen cells for 4 or 12 hours, the 3H-uracil uptake was significantly increased compared with that of control group. From the results, it was inferred that, although the penetration of E. tenella sporozoites into the lymphoid cells such as IEL is not an essential step, it should be at least a beneficial one for the survival and development of sporozoites in the chicken intestine.