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Biomedical subjects

I A Khan

Publications and source records attributed to I A Khan.

At least 19 recordsLinked to original sources
PubMed1995

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.

Animals↗
PubMed1995

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.

Animals↗
PubMed1995

The efferent projections of the periaqueductal gray in the rat: a Phaseolus vulgaris-leucoagglutinin study. I. Ascending projections.

This study has examined the ascending projections of the periaqueductal gray in the rat. Injections of Phaseolus vulgaris-leucoagglutinin were placed in the dorsolateral or ventrolateral subregions, at rostral or caudal sites. From either region, fibers ascended via two bundles. The periventricular bundle ascended in the periaqueductal and periventricular gray matter. At the posterior commissure level, this bundle divided into a dorsal component that terminated in the intralaminar and midline thalamic nuclei, and a ventral component that supplied the hypothalamus. The ventral bundle formed in the deep mesencephalic reticular formation and supplied the ventral tegmental area, substantia nigra pars compacta, and the retrorubral field. The remaining fibers were incorporated into the medial forebrain bundle. These supplied the lateral hypothalamus and forebrain structures, including the preoptic area, the nuclei of the diagonal band, and the lateral division of the bed nucleus of the stria terminalis. The dorsolateral subregion preferentially innervated the centrolateral and paraventricular thalamic nuclei and the anterior hypothalamic area. The ventrolateral subregion preferentially innervated the parafascicular and central medial thalamic nuclei, the lateral hypothalamic area, and the lateral division of the bed nucleus of the stria terminalis. Although the dorsolateral and ventrolateral subregions gave rise to differential projections, the projections from both the rostral and caudal parts of either subregion were similar. This suggests that the dorsolateral and ventrolateral subregions are organized into longitudinal columns that extend throughout the length of the periaqueductal gray. These columns may correspond to those demonstrated in recent physiological studies.

Animals↗
PubMed1995

The efferent projections of the periaqueductal gray in the rat: a Phaseolus vulgaris-leucoagglutinin study. II. Descending projections.

The descending projections of the periaqueductal gray (PAG) have been studied in the rat using the anterograde tracer Phaseolus vulgaris-leucoagglutinin. The tracer was injected into the dorsolateral or ventrolateral subdivisions of the PAG at rostral or caudal sites. It was found that the patterns of the descending projections of the rostral and caudal parts of the dorsolateral PAG were the same and that the patterns of the descending projections of the rostral and caudal parts of the ventrolateral PAG were the same. However, the patterns of projections of the dorsolateral and ventrolateral PAG subregions were substantially different. These results suggest that the dorsolateral and ventrolateral parts of the PAG are organized into longitudinal columns that extend throughout the length of the PAG. The axons of PAG neurons descended through the pons and medulla via two routes. A small fiber bundle was present in the periaqueductal gray and in the periventricular area. This bundle distributed fibers and terminals locally within the periaqueductal gray and in the locus coeruleus and Barrington's nucleus. A larger bundle had a diffuse arrangement in the pontine reticular formation, however, and it had a more restricted distribution in the medulla, where it occupied a position dorsolateral to the pyramid. This bundle supplied structures in the pontine and medullary tegmentum. The dorsolateral column preferentially supplied the locus coeruleus, subcoeruleus, the gigantocellular nucleus pars alpha, the rostral part of the paragigantocellular nucleus, and the region of the A5 noradrenergic cell group. The ventrolateral column preferentially supplied the nucleus raphe magnus, the caudal part of the lateral paragigantocellular nucleus, and the rostroventrolateral reticular nucleus.

Animals↗
PubMed1995

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.

Animals↗
PubMed1995

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.

Acute Disease↗
PubMed1994

Toxoplasma gondii: a monoclonal antibody that inhibits intracellular replication.

During its intracellular life cycle within the infected host cell, Toxoplasma gondii is able to undergo rapid asexual replication. Neither the mechanism by which the parasite initiates this process nor the requirements for maintaining it are understood. We produced a monoclonal antibody, 1B8, that identifies a parasite antigen of approximate M(r) 97 kDa as determined by SDS-PAGE. The epitope recognized by mAb 1B8 appears as a collection of vesicular structures scattered throughout the cell cytoplasm. When RH strain parasites are incubated with mAb 1B8 in the absence of serum complement, parasite growth is inhibited by > 90% as determined by radioisotope incorporation. Both attachment and invasion assays show that neither of these parasite-host cell interactions are inhibited by the mAb. However, a marked reduction in the number of intracellular rosettes was observed following mAb treatment of the parasites. Viable extracellular parasites are able to endocytose mAb 1B8. Once within the parasite cytosol the antibody recognizes the vesicular structures similar to those observed with fixed parasites. Immunofluorescence assays with Besnoitia jellisoni and Plasmodium falciparum show that the epitope recognized by mAb 1B8 is conserved among Coccidiae but not the kinetoplastid Leishmania.

Animals↗
PubMed1993

Antibodies to Toxoplasma gondii major surface protein (SAG-1, P30) inhibit infection of host cells and are produced in murine intestine after peroral infection.

Monoclonal and polyclonal, monospecific antibodies to the major surface antigen of Toxoplasma gondii (SAG-1, P30) inhibit infection of human fibroblasts and murine enterocytes. Fab prepared from polyclonal, monospecific antibody to P30 also have this inhibitory effect on invasion, which indicates that this antibody directly blocks parasite infection of host cells rather agglutinating the parasite. Antibodies to another surface protein (P22) did not alter in vitro infection. If the inhibitory effect of antibody to P30 was due to steric hindrance or complexing of surface epitopes contiguous to P30, antibodies to other surface epitopes would also be inhibitory and they are not. Urea treatment of antibody (which permits discrimination of high and low avidity antibody) did not alter the effect of anti-P30 antibody. This observation indicates that the effect of the antibody to P30 was not an artifact of differences in the avidity of the antibody to P22 and P30. Heat inactivated antisera from mice infected with either RH or PTg strain T. gondii (P30+) inhibit infection of fibroblasts when challenged with autologous wild-type parasites by 87 and 40%, respectively. In contrast, these antisera have little inhibitory effect (13 and 19%, respectively) against infection of human fibroblasts by a P30-deficient mutant (PTgB). Antisera raised to the P30-deficient mutant had no significant effect on infection of cells by wild-type strains that have surface P30. The neoglycoprotein, BSA-glucosamide, competitively blocks infection of human fibroblasts by P30+ tachyzoites with surface P30 in higher level than those without surface P30. This observation indicates that there is likely to be a glycosylated host cell receptor to which T. gondii's major surface Ag SAG-1 (P30) binds. Mice infected perorally develop intestinal IgA antibody to the major 30-kDa epitope of T. gondii. Thus, the major surface epitope of T. gondii, SAG-1 (P30), has an important, functional role in infection of host cells by T. gondii and elicits an intestinal antibody response after peroral infection.

Animals↗
PubMed1992

Antigen-specific (p30) mouse CD8+ T cells are cytotoxic against Toxoplasma gondii-infected peritoneal macrophages.

The importance of CD8+ T cells in immunity against Toxoplasma gondii is now well recognized. The mechanism by which these CD8+ T cells are able to confer this immunity is not yet understood. To examine the Ag specificity of this response, immune splenocytes from mice immunized with p30, a major surface parasite Ag, were evaluated for their ability to lyse peritoneal macrophages infected with three different strains of T. gondii. Macrophages infected with either the RH or P wild-type strain tachyzoites were lysed at varying E:T ratios by nylon wool nonadherent immune splenocytes whereas macrophages infected with a p30-deficient mutant (B mutant) of the P strain were not. The gene encoding p30 for the wild type and B mutant were amplified by the polymerase chain reaction. This revealed a nonsense mutation in the B mutant such that its primary translation product is predicted to be about two-thirds the size of the wild-type p30 molecule. mAb depletion studies indicate that the cytotoxic effect of the immune splenocytes is mediated by the CD8+ T cell population. Peritoneal macrophages infected with the three different strains (RH, P wild type, B mutant) from mice genetically restricted were not lysed by the immune CD8+ effector cell population. A cloned line (C3) of p30 Ag-specific CD8+ T cells exhibited significant cytotoxicity against syngeneic peritoneal macrophages infected with either the RH or P strain tachyzoites. There was no macrophage lysis observed by these CD8+ effector cells of either syngeneic macrophages infected with the B mutant or nonsyngeneic macrophages infected with the three different tachyzoite strains.

Amino Acid Sequence↗
PubMed1992

Stimulatory effects of serotonin on maturational gonadotropin release in the Atlantic croaker, Micropogonias undulatus.

The effects of serotonin (5-HT) injection alone, and in combination with des Gly10 [D-Trp6]-luteinizing hormone-releasing hormone ethylamide (LHRHa), on plasma maturational gonadotropin (GtH) levels in the Atlantic croaker, Micropogonias undulatus, were examined. An injection of 5-HT (20 micrograms/g body wt) alone did not significantly elevate GtH levels, whereas simulatneous administration of LHRHa (20 ng/g body wt) and 5-HT elicited a greater elevation of plasma GtH levels than that induced by LHRHa alone. Pretreatment of 1-year-old fish with fluoxetine (10 micrograms/g), a 5-HT reuptake inhibitor, only slightly augmented the effect of 5-HT on GtH levels, whereas pretreatment with ketanserin (10 micrograms/g), a 5-HT receptor antagonist, completely inhibited the potentiating effect of 5-HT on the GtH response to LHRHa. Administration of LHRHa (20 ng/g) or 5-HT (20 micrograms/g) significantly elevated GtH levels in the 2- and 3-year-old croaker, but the combined treatment failed to increase GtH levels above those induced by LHRHa alone. However, with a lower dose of LHRHa (5 ng/g), the combination produced an additive effect. Serotonin (20 micrograms/ml media) alone, and in combination with LHRHa (10 ng/ml media), significantly stimulated GtH release from the pituitaries of gonadally mature 2- and 3-year-old female croaker during an 18-hr incubation in vitro, but not from pituitaries of gonadally regressed fish. The combined treatment of LHRHa with 5-HT also significantly stimulated in vitro GtH release during 6- and 12-hr pituitary incubations, whereas these treatments alone were ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1992

Tubulin structure and biochemistry.

In the past year, much has been learned about structure-function correlations in the tubulin molecule, and specifically about the nature and roles of post-translational modifications and tubulin isotypes. The interactions between tubulin and its ligands--both microtubule-associated proteins and anti-mitotic drugs--are becoming clearer at the molecular level.

Animals↗
PubMed1992

New phenolic glucosides from the leaves of Eurya tigang.

Three new compounds, 6'-O-coumaroyl-1'-O-[2-(4-hydroxyphenyl)ethyl]-beta-D-glucopyra nos ide [1] (eutigoside A), 6'-O-coumaroyl-1'-O-[2-(1-hydroxy-4-oxo-2,5-cyclohexadien-1- yl)ethyl]-beta-D-glucopyranoside [2] (eutigoside B), and 6'-O-cinnamoyl-1'-O-[2-(1-hydroxy-4-oxo-2,5-cyclohexadien-1-yl)eth yl]- beta-D-glucopyranoside [3] (eutigoside C) have been isolated from the leaves of Eurya tigang, along with other known compounds (afzelin, quercitrin, p-coumaric acid, methyl-alpha-D-fructofuranoside, isorengyol, and euryanoside). Their structures were determined by chemical and spectroscopic methods (uv, ir, ms, 1H-1H COSY, and 1H-13C COSY).

Animals↗
PubMed1991

A purified parasite antigen (p30) mediates CD8+ T cell immunity against fatal Toxoplasma gondii infection in mice.

Induction of protective immunity against acute and chronic toxoplasmosis can be achieved using p30, the major membrane and excreted/secreted protein of Toxoplasma gondii. This protein, when administered to outbred mice in the presence of the saponin Quil A, is able to induce almost 100% protection against acute infection without evidence of intracerebral cyst development. Adoptive transfer of immune splenocytes from immunized inbred A/J mice conferred a significant level (p less than 0.001) of protection against subsequent challenge. Phenotypic analysis in outbred as well as two different strains of inbred mice (A/J and C57BL/6) demonstrated that CD8+ T cells are selectively stimulated by this immunization protocol. T cell depletion studies using specific mAb directed at either CD3+ or CD8+ T cell phenotype, followed by adoptive transfer, failed to confer protective immunity, whereas CD4+ depletion had no effect. These cytotoxic CD8+ T cells produced high titers of both IFN-gamma and IL-2. Moreover, these CD8+ T cells were directly parasiticidal against radiolabeled extracellular T. gondii, further supporting the critical immune function of these p30 Ag-specific CD8+ T cells in host immunity against T. gondii infection.

Adjuvants, Immunologic↗
PubMed1991

Possible regulation of the in vitro assembly of bovine brain tubulin by the bovine thioredoxin system.

Microtubule assembly in vitro and in vivo is highly sensitive to a variety of sulfhydryl-reactive reagents, raising the question of the possible existence of a physiological sulfhydryl-mediated system for regulating microtubule assembly. However, the specific reagents which have previously been used to inhibit microtubule assembly in vitro are either nonphysiological or, if physiological, effective only at concentrations much higher than their physiological ones. Because of reports of association in vivo between microtubules and the sulfhydryl-reactive proteins thioredoxin and thioredoxin reductase, we decided to examine the interaction in vitro between microtubules and the thioredoxin system, comprising thioredoxin, thioredoxin reductase and NADPH. At pH 6.8, both the mammalian and the Escherichia coli thioredoxin systems inhibited microtubule assembly by 4-35% (19 +/- 9%) by reducing one intra-subunit disulfide bond in the tubulin dimer. The thioredoxin-reducible disulfide of the tubulin dimer remains protected from thioredoxin in the assembled microtubules. Thioredoxin or thioredoxin reductase alone, or together in the absence of NADPH, were incapable of either reducing tubulin or inhibiting microtubule assembly. Microtubules formed from reduced tubulin were found to be stable and morphologically identical to those obtained from native tubulin dimers. Since the components of the thioredoxin system were used at concentrations similar to their physiological ones, our results suggest a potential role of the thioredoxin system in regulation of microtubule assembly in vivo.

Animals↗
PubMed1991

Changes in hypothalamic monoamine oxidase activity in relation to 17 beta-estradiol and clomiphene citrate treatments in the teleost Channa punctatus during three seasons.

Hypothalamic monoamine oxidase (MAO) activity displayed biphasic responses to administration of estradiol-17 beta (E2) depending on season. Lower doses of 0.05 and 0.10 microgram/g BW of E2 had enhanced enzyme activity and higher doses (0.5 and 1.0 microgram/g BW) depressed it significantly in preparatory season. In prespawning phase, the lowest dose of 0.05 microgram/g BW of E2 was stimulatory and the higher doses were inhibitory to MAO activity. In postspawning season, lower doses (0.05 and 0.10 microgram/g BW) of E2 failed to elicit any significant change in enzyme activity whereas the higher doses (0.5 and 1.0 microgram/g BW) elevated it significantly. Administration of clomid (5, 10, and 20 micrograms/g BW) inhibited MAO activity in a dose-dependent manner during all the three seasons. The results show that E2 may participate in feedback control of gonadotropin secretion by modifying monoaminergic activity at the level of oxidative deamination by MAO.

Animals↗
PubMed1991

Pineal-gonadal relationship in the teleost Channa punctatus (Bloch): evidence for possible involvement of hypothalamic serotonergic system.

In Channa punctatus, pinealectomy results in an accelerated growth (stimulatory effect) of the ovary in preparatory phase (March), but had no significant effect in prespawning (May-June) or postspawning (September) phases. Administration of melatonin (25 micrograms/fish or 0.4 mg/kg BW at 2-day intervals for 30 days) inhibits the stimulatory effect of a long photoperiod and high temperature (16L:8D; 22 +/- 1 degree C) on the ovary in the early preparatory phase (February). In the late preparatory phase (April), the administration of both melatonin (0.5 mg/kg BW at 2-day intervals) and parachlorophenylalanine (pCPA, a serotonin synthesis blocker; 100 mg/kg BW at 3-day intervals) for 30 days inhibits ovarian activity in comparison to that of the saline-treated control group. In the dose-response study, greater than or equal to 0.5 mg/kg BW of melatonin induced a significant increase in hypothalamic 5-HT content and greater than or equal to 10 mg/kg BW of pCPA decreased it significantly. In the time-course study, melatonin (2.0 mg/kg BW) elevates the 5-HT content significantly after an hr of the injection and maintained it up to 48 hrs. The administration of pCPA (200 mg/kg BW) had significantly inhibited the 5-HT content which was sustained for 72 hr. In another study, a single injection of melatonin (0.5 mg/kg BW) increased the 5-HT content significantly. A single injection of pCPA (100 mg/kg BW) decreased significantly both the content and activity of 5-HT. It is inferred that hypothalamic 5-HT may play a central role in photosexual mechanisms and mediate long photoperiodic effects on neuroendocrine-reproductive axis.

Animals↗
PubMed1990

Selective osmotic effect on diffusion of plasma membrane lipids in maize protoplasts.

Osmotic levels in the range typically used during plant protoplast isolation and incubation were investigated with regard to effects on the lateral diffusion of lipid probes in the plasma membrane. The lateral diffusion coefficient of a fluorescent sterol probe in the plasma membrane of maize (Zea mays L.) root protoplasts in a medium containing 0.45 M mannitol was 4 times faster than when the medium contained 0.9 M mannitol. The lateral diffusion coefficient of a fluorescent phospholipid probe, however, did not change over this range of mannitol concentrations. Similar diffusion characteristics were observed when the medium contained trehalose instead of mannitol. Slower lateral diffusion of the sterol probe at higher osmolality was also observed when KCl/CaCl2-based osmotic media were used with protoplasts isolated by a mechanical, rather than by an enzymic, method. Extraction and quantitation of total lipids from protoplasts showed that both the phospholipid and sterol contents per protoplast decreased with increasing osmolality, while the sterol/phospholipid ratio increased. These results demonstrate that osmotic stress induces selective changes in both the composition and biophysical properties of plant membranes.

Cell Membrane↗