Aroclor 1254-induced alterations in hypothalamic monoamine metabolism in the Atlantic croaker (Micropogonias undulatas): correlation with pituitary gonadotropin release

Male Atlantic croaker (Micropogonias undulatus) were exposed to Aroclor 1254 (a PCB mixture) in the diet (0.1 mg/100 g body wt./day) for 30 days during gonadal recrudescence to investigate the effects of the PCB mixture on reproductive neuroendocrine function. The concentrations of biogenic amines (epinephrine [E], norepinephrine [NE], dopamine [DA], and 5-HT) and their major metabolites (3,4-dihydroxyphenylacetic acid [DOPAC], 3-methoxytyramine [3-MT], homovanillic acid [HVA], and 5-hydroxyindolacetic acid [5-HIAA]) were measured in the preoptic-anterior hypothalamus (POAH) and medial and posterior hypothalamus (MPH) using HPLC with electrochemical detection. There was a significant decline in 5-HT and DA concentrations and an increase in their metabolite to parent amine ratios in both the POAH and MPH of Aroclor 1254-exposed fish. In addition, Aroclor 1254 exposure resulted in the loss of the in vitro pituitary gonadotropic response to stimulation by a luteinizing hormone-releasing hormone analog (LHRHa). We have previously shown that 5-HT modulates the gonadotropin release in response to LHRHa in Atlantic croaker. Therefore, the reduced availability of neuronal 5-HT may be at least partially responsible for the loss of the gonadotropic response to stimulation by LHRHa.

Taxol differentially modulates the dynamics of microtubules assembled from unfractionated and purified beta-tubulin isotypes

Substoichiometric binding of taxol to tubulin in microtubules potently suppresses microtubule dynamics, which appears to be the most sensitive antiproliferative mechanism of taxol. To determine whether the beta-tubulin isotype composition of a microtubule can modulate sensitivity to taxol, we measured the effects of substoichiometric ratios of taxol bound to tubulin in microtubules on the dynamics of microtubules composed of purified alphabeta(II)-, alphabeta(III)-, or alphabeta(IV)-tubulin isotypes and compared the results with the effects of taxol on microtubules assembled from unfractionated tubulin. Substoichiometric ratios of bound taxol in microtubules assembled from purified beta-tubulin isotypes or unfractionated tubulin potently suppressed the shortening rates and the lengths shortened per shortening event. Correlation of the suppression of the shortening rate with the stoichiometry of bound taxol revealed that microtubules composed of purified alphabeta(II)-, alphabeta(III)-, and alphabeta(IV)-tubulin were, respectively, 1.6-, 7.4-, and 7.2-fold less sensitive to the effects of bound taxol than microtubules assembled from unfractionated tubulin. These results indicate that taxol differentially modulates microtubule dynamics depending upon the beta-tubulin isotype composition. The results are consistent with recent studies correlating taxol resistance in tumor cells with increased levels of beta(III0- and beta(IV)-tubulin expression and suggest that altered cellular expression of beta-tubulin isotypes can be an important mechanism by which tumor cells develop resistance to taxol.

Antifungal activity of a new triterpenoid glycoside from Pithecellobium racemosum (M.)

PURPOSE

In a continuation of our search for novel antifungal compounds from higher plants, the standard extract of the bark of Pithecellobium racemosum was found to have good activity against important AIDS-related opportunistic yeasts.

METHODS

The extract was subjected to bioguided fractionation using silica gel column chromatography which led to purification of triterpene glycosides. The structures of these compounds were determined by a combination of spectroscopic (IR, NMR, HRMS) and chemical methods.

RESULTS

Compound 1 is a new glycoside, 3-O[alpha-L-arabinopyranosyl (1-2)][alpha-L arabinopyranosyl (1-6)]2-acetoamido-2-deoxy-beta-D-glucopyranosyl oleanolic acid and Compound 2 was identified as the known compound 3-O-[alpha-L-arabinopyranosyl (1-2)]alpha-L-arabinopyranosyl (1-6)] 2-acetamido-2-deoxy-beta-D-glucopyranosyl echinocystic acid.

CONCLUSIONS

Compound 1 is a new glycoside, 3-O-[alpha-L-arabinopyranosyl (1-2)]alpha-L-arabinopyranosyl (1-6)]-2-acetoamido-2-deoxy-beta-D-glucopyranosyl oleanolic acid and exhibits moderate antifungal activity against T. mentogrophytes, C. albicans and S. cerevisiae with MIC values of 6.25, 12.5 and 12.5 micrograms/ml respectively.

Neospora caninum: role for immune cytokines in host immunity

Neospora caninum is a coccidial protozoan parasite that infects a large range of mammals including dogs, cats, mice, and cattle. Morphologically, N. caninum appears indistinguishable from Toxoplasma gondii, although they are genetically distinct. To date there have been no reported cases of this infection in humans, although nonhuman primates may be susceptible to infection. Inbred A/J mice develop no clinical and little histologic evidence of infection in spite of a high-dose inoculum of N. caninum. Splenocytes obtained from infected mice proliferate in vitro in response to both N. caninum and T. gondii-soluble antigen. A transient state of T cell hyporesponsiveness to parasite antigen and mitogen was observed at Day 7 p.i. This downregulatory response could be partially reversed by the addition of the nitric oxide antagonist LNMMA, but not antibody to IL-10. Mice infected with N. caninum produce significant quantities of IL-12 and IFN gamma, most evident shortly after infection. In vivo, antibody to IL-12 is able to neutralize immune resistance to the parasite. Moreover, in vivo depletion of IFN gamma with antibody renders the mice susceptible to infection. These observations suggest that N. caninum induces a T cell immune response in the infected host that is at least partially mediated by IL-12 and IFN gamma.

Paediatric prescribing in Karachi

To assess amount of drug overuse we studied drug prescribing for common childhood problems by 65 general practitioners (GPs) and 29 paediatricians. A total of 2433 encounters between GPs or paediatricians and children under five years of age were observed. The presenting complaints were fever in 18%, cough in 9%, both fever and cough in 21%, vomiting in 20% and diarrhoea in 41% of encounters. Antibacterials were prescribed in 49% of encounters, analgesics and antipyretics in 29%, antiemetics in 8% and injectables in 15%. Antidiarrhoeals were prescribed in 41% encounters with children reported to have diarrhoea. Ampicillin and cotrimoxazole were the two common antibacterials prescribed by both GPs and paediatricians. Antibacterials were prescribed in significantly larger number of encounters with GPs than in those with paediatricians. Mean encounter time of patients with GPs was 3.4+/-2.7 minutes and with paediatricians 9.7+/-4.1 minutes.

Induction of gammadelta T cells during acute murine infection with Toxoplasma gondii

The importance of the host gammadelta T cell response to microbial pathogens is not yet fully understood. We report that inbred mice infected with T. gondii developed a gammadelta T cell proliferative response to parasite Ag. Mice depleted of either the alphabeta or gammadelta TCR were found to be significantly more susceptible to infection than the parent mouse strain. Proliferation of gammadelta T cells was observed in mice deficient in the TCR-alphabeta in response to UV-irradiated parasites. These T cells lyse parasite-infected syngenic macrophages. Adoptive transfer of these gammadelta T cells into beta2 microglobulin-deficient mice that have been depleted of both CD4+ and NK cells prolongs survival against acute parasite challenge when compared with nontransferred controls. The gammadelta T cells isolated from infected alpha -/- mice express a 10-fold increase in mRNA and produce high titers of IFN-gamma. These data suggest that gammadelta T cells may play an important role in the early host response to infection with T. gondii.

Induction of gammadelta T cells during acute murine infection with Toxoplasma gondii

The importance of the host gammadelta T cell response to microbial pathogens is not yet fully understood. We report that inbred mice infected with T. gondii developed a gammadelta T cell proliferative response to parasite Ag. Mice depleted of either the alphabeta or gammadelta TCR were found to be significantly more susceptible to infection than the parent mouse strain. Proliferation of gammadelta T cells was observed in mice deficient in the TCR-alphabeta in response to UV-irradiated parasites. These T cells lyse parasite-infected syngenic macrophages. Adoptive transfer of these gammadelta T cells into beta2 microglobulin-deficient mice that have been depleted of both CD4+ and NK cells prolongs survival against acute parasite challenge when compared with nontransferred controls. The gammadelta T cells isolated from infected alpha -/- mice express a 10-fold increase in mRNA and produce high titers of IFN-gamma. These data suggest that gammadelta T cells may play an important role in the early host response to infection with T. gondii.

A preliminary study of fingerprinting of Pseudomonas aeruginosa by whole cell protein analysis by SDS-PAGE

Forty two strains of Pseudomonas aeruginosa isolated from bronchoalveolar lavage fluid from intubated patients admitted to the Intensive care unit in AIIMS between December 1993 to June 1994 were included in the study. After obtaining typical biochemical profile, antimicrobial susceptibility was performed against ceftazidime, amikacin, gentamicin, ampicillin, cefotaxime and ciprofloxacin. Pyocin typing of these 42 strains was performed by scrape and streak method using 22 indicator strains. Forty strains could be typed showing excellent discrimination but on repeated testing the group designation changed indicating that the system had low reproducibility. SDS-PAGE of whole cell protein profile indicated the presence of 45 protein bands of different molecular weights, individual isolates had 37 to 42 protein band ranging in molecular weight from 340 kDa to 14.3 kDa. On the basis of Dice index of similarity the strains could be grouped into 20 types. Since all strains could be typed, the system has adequate typability. Similar results were obtained on repeated testing indicating good reproducibility.

Application of whole cell protein analysis by SDS PAGE to establish the source of Salmonella typhimurium

Salmonella typhimurium isolated from an infant and the powder milk as well as from three different epidemiologically unrelated patients had the same biochemical reactions, antibiogram, serotype and all were non-typable by phage typing. The clonal nature of epidemiologically related isolates was established by SDS PAGE analysis.

Melatonin influences gonadotropin II secretion in the Atlantic croaker (Micropogonias undulatus)

The role of melatonin in the control of gonadotropin II (GtH II) secretion was investigated in Atlantic croaker (Micropogonias undulatus) during different phases of the day-night cycle and seasonal reproductive cycle. Intraperitoneal injection of melatonin during the late-light phase of the day-night cycle elicited a significant elevation in plasma GtH II levels in croaker with fully developed gonads. The increase in GtH II levels was observed 30 min postinjection; the levels remained elevated for 1 hr and started to decline at the 2-hr sampling time. The stimulatory effect of melatonin was dose-dependent over the range 5 to 500 ng/g body weight. Circulating GtH II levels in fish with fully developed gonads showed significant diurnal variation, with elevated levels during the dark phase. The GtH II secretion in response to stimulation by a LHRH analog (LHRHa) also varied during the day-night cycle, with the maximum levels during the early-dark phase. Interestingly, melatonin stimulated GtH II release during the late-light and early- and mid-dark phases. The increased gonadotropic response to melatonin preceded (late-light phase) or corresponded to the period of elevated circulating GtH II levels and increased responsiveness to stimulation by LHRHa during the dark phase, suggesting that melatonin may be involved in the control of daily GtH II cycles in this species. Melatonin inhibited LHRHa-induced GtH II release during the mid-dark phase of the day-night cycle in a dose-dependent manner; the physiological significance of this inhibitory influence is not understood at present. No significant effect of melatonin on basal or LHRHa-induced GtH II release was observed in regressed croaker. Melatonin injection (1 or 10 ng/g body weight) into the third ventricle in the preoptic anterior hypothalamic area (POAH) of croaker with fully developed gonads resulted in an elevation in plasma GtH II concentrations. In addition, a low concentration (0.2 ng/ml) of melatonin stimulated in vitro GtH II release from the pituitary fragments of fish with fully developed gonads. These results suggest that melatonin can influence GtH II secretion by acting at the level of POAH and also directly at the pituitary to stimulate GtH II release.

Self-reported concepts about oral rehydration solution, drug prescribing and reasons for prescribing antidiarrhoeals for acute watery diarrhea in children

Sixty-seven general practitioners (GPs) and 27 paediatricians practising in Karachi were interviewed to evaluate their knowledge and attitude towards use of oral rehydration solution (ORS) and management of acute watery diarrhoea (AWD) in children and to define factors for their self-reported prescribing of antidiarrhoeals. Whilst nearly 50% of them reported ORS to be palatable and acceptable by children, 80% reported that ORS was not accepted by parents as sole treatment. Eighty per cent of GPs and 37% of paediatricians reported prescribing antidiarrhoeals for AWD in children, and 'parental pressure' and 'use as placebo' were the commonest reasons. In addition 45% of GPs believed in the efficacy of antidiarrhoeals and thought these drugs necessary for the control of diarrhoea.

IL-15 augments CD8+ T cell-mediated immunity against Toxoplasma gondii infection in mice

Cytokines of the Th1 profile are important mediators of protective host immunity against Toxoplasma gondii infection in mice. In this study we describe the effect of the recently identified cytokine, IL-15, on prevention of murine infection with T. gondii. Administration of exogenous rIL-15 with soluble Toxoplasma lysate Ag (TLA) provides complete protection against a lethal parasite challenge, whereas treatment with either rIL-15 or TLA alone is not protective. Following immunization with TLA/rIL-15, there is a significant proliferation of splenocytes expressing the CD8+ phenotype in response to TLA. A significant rise in the level of serum IFN gamma was observed in vaccinated mice. Adoptive transfer of CD8+ T cells, but not CD4+ T cells, from TLA/rIL-15-vaccinated mice protects naive mice from a lethal parasite challenge. These CD8+ T cells exhibit enhanced CTL activity against target macrophages infected with T. gondii. Mice that have been immunized are protected against lethal parasite challenge for at least 1 mo postvaccination. These observations demonstrate that TLA when administered with exogenous rIL-15 generates toxoplasmacidal Ag-specific CD8+ T cells. These T cells proliferate upon exposure to parasite Ag, exhibit long term memory CTL against infected target cells, and may be involved in host immune memory to this parasite.

IL-15 augments CD8+ T cell-mediated immunity against Toxoplasma gondii infection in mice

Cytokines of the Th1 profile are important mediators of protective host immunity against Toxoplasma gondii infection in mice. In this study we describe the effect of the recently identified cytokine, IL-15, on prevention of murine infection with T. gondii. Administration of exogenous rIL-15 with soluble Toxoplasma lysate Ag (TLA) provides complete protection against a lethal parasite challenge, whereas treatment with either rIL-15 or TLA alone is not protective. Following immunization with TLA/rIL-15, there is a significant proliferation of splenocytes expressing the CD8+ phenotype in response to TLA. A significant rise in the level of serum IFN gamma was observed in vaccinated mice. Adoptive transfer of CD8+ T cells, but not CD4+ T cells, from TLA/rIL-15-vaccinated mice protects naive mice from a lethal parasite challenge. These CD8+ T cells exhibit enhanced CTL activity against target macrophages infected with T. gondii. Mice that have been immunized are protected against lethal parasite challenge for at least 1 mo postvaccination. These observations demonstrate that TLA when administered with exogenous rIL-15 generates toxoplasmacidal Ag-specific CD8+ T cells. These T cells proliferate upon exposure to parasite Ag, exhibit long term memory CTL against infected target cells, and may be involved in host immune memory to this parasite.

Activation-mediated CD4+ T cell unresponsiveness during acute Toxoplasma gondii infection in mice

Infection of mice with Toxoplasma gondii has been shown to induce a transient state of immune down-regulation. Earlier reports have demonstrated the role of cytokines, in particular IL-10, in this host response. Here evidence is presented that T. gondii, a major opportunistic pathogen of the newborn and those with AIDS, is able to induce CD4(+) T cell apoptosis in the infected murine host. We have examined the changes in the CD4(+) T cell population that occur during acute infection in an experimental mouse model. Seventy-six percent of the CD4(+) T cell population increased in volume by day 7 post-infection and expressed T cell maturation markers (CD44(hi), IL-2Rhi, Mel-14(lo)). Further noted was a clonal activation of several CD4(+) T cell to mitogen or parasite antigen stimulation was observed, in particular Vbeta5 T cells. Addition of rIL-2 partially restored the CD4(+) T cell proliferative response in vitro. The T cell activation marker CTLA-4 could not be detected and the co-stimulatory molecule, CD28, was down-regulated. Electrophoretic and morphologic analysis of these cells post-culture demonstrated a DNA fragmentation pattern and cell death consistent with apoptosis. These studies demonstrate for the first time in a protozoan parasite that activation induced CD4(+) T cell unresponsiveness occurs during acute T. gondii infection in mice, and may be important in immune down-regulation and parasite persistence in the infected host.

Solitary fibrous tumour arising in the nasal cavity: report of a case

The nasal and the paranasal sinuses are a rare site for solitary fibrous tumours. There have been no previously reported cases in the English literature, with eight cases in the world literature (Witkin and Rosai, 1991; Zuckerberg et al., 1991). We present a case of a solitary fibrous tumour arising in the nasal cavity and review the previous reports.

Drug prescribing practices of general practitioners and paediatricians for childhood diarrhoea in Karachi, Pakistan

Observations were made of 996 encounters between children with diarrhoea and practitioners (28 paediatricians, 62 general practitioners) in Karachi, Pakistan. Oral rehydration salt (ORS) was prescribed in more than 50% of encounters by 53% of general practitioners (GPs) and 61% of paediatricians. Sixty-six percent of GPs and 50% of paediatricians prescribed antibacterials, 60% of GPs and 28% of paediatricians prescribed antidiarrhoeals and 39% of GPs and 32% of paediatricians prescribed antiamoebics in more than 30% of their encounters. Looking at all the encounters, we observed that ORS was prescribed in 52 and 51%, antibacterials in 41 and 36%, antidiarrhoeals in 48 and 29%, and antiamoebics in 26 and 22% of encounters by GPs and paediatricians, respectively, Cotrimoxazole was the most frequently prescribed antibacterial by both types of practitioners. Antidiarrhoeals were prescribed more often by GPs than by paediatricians. In 77% of their encounters, GPs dispensed drug formulations known as "mixtures' made in their own dispensing corners. The mean duration of encounters between patients and GPs was 3 +/- 2 minutes and between patients and paediatricians was 9 +/- 4 minutes. These results indicate inadequate prescription of ORS and excessive prescription of antibacterials, antidiarrhoeals and antiamoebics. Intervention strategies need to be planned to improve the prescribing practices of both groups.

Phosphorylation of beta III-tubulin

There is considerable evidence that mammalian beta-tubulin is phosphorylated. Specifically, of the seven beta isotypes, the phosphorylated one is beta III, the isotype found almost entirely in neurons. The phosphate is added at a serine and perhaps a tyrosine near the C-terminus. All the evidence to date has been gathered by growth of cells and tissues in the presence of radioactive inorganic phosphate followed by tubulin isolation and determination of the labeled tubulin; thus, the actual extent of phosphorylation of beta III is unknown. Nor is it known if alpha-tubulin and the other beta isotypes are phosphorylated by a mechanism which would not be revealed by previous experiments. In addition, the role of tubulin phosphorylation is unknown. We have purified the alpha beta II-, alpha beta III-, and alpha beta IV-tubulin dimers from bovine brain and have determined their phosphate content chemically. We have found that alpha-tubulin is not phosphorylated and neither are the beta II or beta IV isotypes. However, beta III is phosphorylated with a stoichiometry of about 1.52 mol/mol. We have found that the phosphate on beta III is resistant to a wide variety of phosphatases except for human erythrocyte phosphatase 2A and that removal of the phosphate inhibits microtubule assembly in vitro stimulated by microtubule-associated protein 2 (MAP 2). However such an inhibition was not evident when microtubule assembly was induced in the absence of microtubule-associated proteins. Our results suggest the possibility that beta III phosphorylation may play a role in regulating microtubule assembly in vivo.

Production of nitric oxide (NO) is not essential for protection against acute Toxoplasma gondii infection in IRF-1-/- mice

Production of nitric oxide (NO) by macrophages is important for the killing of intracellular pathogens. IFN-gamma and LPS stimulate NO production by transcriptional up-regulation of inducible nitric oxide synthetase (iNOS). In the present study we used mice with a targeted disruption of the IFN regulatory factor-1 gene (IRF-1-/-) to investigate the importance of NO in the host immune response against Toxoplasma gondii, a major cause of infection in newborns and those with AIDS. IRF-1-/- mice were more susceptible to acute Toxoplasma infection, and treatment with either exogenous IFN-gamma or in vivo neutralization of endogenous IFN-gamma had little effect on their susceptibility to infection. However, administration of exogenous IL-12 was able to prolong survival even when IFN-gamma was depleted. An in vivo depletion study suggested that the mechanism of this protective response is mediated in part by CD4+ T cells. The administration of IL-12 could not overcome the inhibition of lymphoproliferative response in T. gondii-infected mice and treatment with N-monomethyl-L-arginine (L-NMMA), a nitric oxide synthase (iNOS) antagonist in vitro was unable to reverse the immunosuppression. In response to Toxoplasma infection, splenocytes from IRF-1-/- mice exhibited increased production of IL-10 as well as a 30-fold increase in its message expression. These studies indicate that NO may not be essential for host immunity to the parasite, and moreover that IL-12 appears to induce an IFN-gamma-independent mechanism of protection against this opportunistic pathogen.

Production of nitric oxide (NO) is not essential for protection against acute Toxoplasma gondii infection in IRF-1-/- mice

Production of nitric oxide (NO) by macrophages is important for the killing of intracellular pathogens. IFN-gamma and LPS stimulate NO production by transcriptional up-regulation of inducible nitric oxide synthetase (iNOS). In the present study we used mice with a targeted disruption of the IFN regulatory factor-1 gene (IRF-1-/-) to investigate the importance of NO in the host immune response against Toxoplasma gondii, a major cause of infection in newborns and those with AIDS. IRF-1-/- mice were more susceptible to acute Toxoplasma infection, and treatment with either exogenous IFN-gamma or in vivo neutralization of endogenous IFN-gamma had little effect on their susceptibility to infection. However, administration of exogenous IL-12 was able to prolong survival even when IFN-gamma was depleted. An in vivo depletion study suggested that the mechanism of this protective response is mediated in part by CD4+ T cells. The administration of IL-12 could not overcome the inhibition of lymphoproliferative response in T. gondii-infected mice and treatment with N-monomethyl-L-arginine (L-NMMA), a nitric oxide synthase (iNOS) antagonist in vitro was unable to reverse the immunosuppression. In response to Toxoplasma infection, splenocytes from IRF-1-/- mice exhibited increased production of IL-10 as well as a 30-fold increase in its message expression. These studies indicate that NO may not be essential for host immunity to the parasite, and moreover that IL-12 appears to induce an IFN-gamma-independent mechanism of protection against this opportunistic pathogen.

IL-7 stimulates protective immunity in mice against the intracellular pathogen, Toxoplasma gondii

Cytokines, in particular IFN-gamma and IL-12, are important in host protection against infection with Toxoplasma gondii. This parasite is a major cause of congenital infection and morbidity in immunosuppressed persons, especially those with AIDS. IL-7, a monomeric protein produced by bone marrow stromal cells and fetal thymus, is able to induce the proliferation of pro-B cells and CD4+ and CD8+ T cells, and to enhance cytotoxicity of CTL and NK cells. Inbred mice were infected with a lethal dose of T. gondii and given IL-7 twice daily. Mice treated with IL-7 beginning at the time of infection survived, whereas mice either treated after infection or not treated died. Phenotypic analysis of splenocytes identified an expansion of NK (asialo GM1+) cells and CD8+ T cell populations. In vivo depletion of NK (asialo GM1+) and CD8+ T cells showed that cells expressing these phenotypes were important for maintaining protection against the parasite. IFN-gamma depletion resulted in complete reversal of the protective effect of IL-7 administration. In vivo depletion of endogenous IL-7 enhanced susceptibility to infection. Cytokine analysis by semiquantitative reverse-transcriptase PCR showed that IL-7 enhances the IFN-gamma response and furthermore reverses the parasite-mediated down-regulatory response on IL-2. These observations indicate that exogenous administration of human rIL-7 is able to protect mice against acute parasite challenge by stimulating IFN-gamma production and augmenting the CD8+ T cell-mediated CTL response.

IL-7 stimulates protective immunity in mice against the intracellular pathogen, Toxoplasma gondii

Cytokines, in particular IFN-gamma and IL-12, are important in host protection against infection with Toxoplasma gondii. This parasite is a major cause of congenital infection and morbidity in immunosuppressed persons, especially those with AIDS. IL-7, a monomeric protein produced by bone marrow stromal cells and fetal thymus, is able to induce the proliferation of pro-B cells and CD4+ and CD8+ T cells, and to enhance cytotoxicity of CTL and NK cells. Inbred mice were infected with a lethal dose of T. gondii and given IL-7 twice daily. Mice treated with IL-7 beginning at the time of infection survived, whereas mice either treated after infection or not treated died. Phenotypic analysis of splenocytes identified an expansion of NK (asialo GM1+) cells and CD8+ T cell populations. In vivo depletion of NK (asialo GM1+) and CD8+ T cells showed that cells expressing these phenotypes were important for maintaining protection against the parasite. IFN-gamma depletion resulted in complete reversal of the protective effect of IL-7 administration. In vivo depletion of endogenous IL-7 enhanced susceptibility to infection. Cytokine analysis by semiquantitative reverse-transcriptase PCR showed that IL-7 enhances the IFN-gamma response and furthermore reverses the parasite-mediated down-regulatory response on IL-2. These observations indicate that exogenous administration of human rIL-7 is able to protect mice against acute parasite challenge by stimulating IFN-gamma production and augmenting the CD8+ T cell-mediated CTL response.

Structure of tubulin at 6.5 A and location of the taxol-binding site

Tubulin, the major component of microtubules, is a heterodimer of two chains, alpha and beta, both of relative molecular mass 50,000 (Mr50K) and with 40-50% identity. The isotypic variety and conformational flexibility of tubulin have so far made it impossible to obtain crystals for X-ray work. Structural knowledge of tubulin has been limited to about 20 A from X-ray diffraction of oriented microtubules, and from electron microscopy of microtubules and zinc-induced crystalline sheets in negative stain. The sheets consist of protofilaments similar to those in microtubules but associated in an antiparallel arrangement, and their two-dimensional character is ideal for high-resolution electron microscopy. Here we present a three-dimensional reconstruction of tubulin to 6.5 A resolution, obtained by electron crystallography of zinc-induced two-dimensional crystals of the protein. The alpha- and beta-subunits appear topologically similar, in agreement with their sequence homology. Several features can be defined in terms of secondary structure. An apparent alpha-helical portion, adjacent to both interdimer and inter-protofilament contacts, is tentatively attributed to a segment near the carboxy terminus of the protein. We can assign the alpha- and beta-subunits on the basis of projection studies of the binding of taxol, which show one taxol site per tubulin heterodimer, in agreement with the known stoichiometry of taxol in microtubules. These studies indicate that taxol affects the interaction between protofilaments; to our knowledge, this is the first time that a ligand-binding site has been visualized in the tubulin molecule.

IL-10 mediates immunosuppression following primary infection with Toxoplasma gondii in mice

Suppression of the host immune response by Toxoplasma gondii has been observed in both human and experimental murine infection. In this study, inbred mice were infected with T. gondii. At day 7 post-infection, the lymphoproliferative response to both mitogen and superantigen as well as parasite antigen were found to be significantly depressed. Using a transwell system, it was determined that the reduced proliferative response was due to soluble factor(s) being expressed by splenocytes from the infected mice. Isolation of the splenocytes into an adherent and nonadherent population suggested that both macrophages and T cells were able to produce at least one soluble factor. Tissue culture supernatant derived from the splenocytes of the infected mice contain increased levels of IL-10, whereas measurable IL-2 levels could not be quantitated. At day 7 post-infection, both a biologic assay for IFN-gamma in culture supernatant and the expression of IFN-gamma mRNA in the splenocytes were reduced. Antibody to IL-10 was able to partially neutralize (almost 50%) the in vitro immune downregulation of the tissue culture supernatant. Anti-IL-10 in combination with a nitric oxide (NO) antagonist was able to reverse the inhibitory activity of the culture supernatant by 85%. Since IL-10 is a potent antagonist of IFN-gamma, it may represent a critical cytokine involved in mediating T. gondii induced immunosuppression in the infected host.

Differences in self-reported and observed prescribing practice of general practitioners and paediatricians for acute watery diarrhoea in children of Karachi, Pakistan

Practice of 60 general practitioners (GPs) and 26 paediatricians for acute watery diarrhoea in children was observed. Later, these GPs and paediatricians were interviewed to record their self-reported prescribing behaviour. Fifty-two percent of the GPs and 12% of the paediatricians reported to prescribe antibiotics, but 77% of the GPs and 85% of the paediatricians were observed prescribing antibiotics for acute watery diarrhoea. Regarding antiamoebics, no difference was seen in number of self-reporting and observed GPs, but significant difference was seen in paediatricians. Of the paediatricians, only 12% reported to prescribe, but 62% were observed prescribing antiamoebics. Similarly, kaolin compounds were observed to be prescribed by smaller number of GPs (63%) than self-reporting ones (80%). Of the paediatricians, 31% reported to prescribe but 38% were observed prescribing kaolin compounds. These results show differences between self-reported and observed drug prescribing practices for acute watery diarrhoea in children. This difference was much wider in paediatricians than in GPs.