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Biomedical subjects

S D Sharma

Publications and source records attributed to S D Sharma.

At least 91 records · Page 5Linked to original sources
PubMed1989

Cloning of cDNAs encoding a 28 kilodalton antigen of Toxoplasma gondii.

By screening cDNA libraries in lambda gt11 with antibodies raised against the previously described protective F3G3 antigen of Toxoplasma gondii, and subsequently screening with nucleic acid probes, we have isolated cDNA clones that encode a 28 kDa antigen of T. gondii that is likely one of the two antigenic components of the F3G3 antigen. The gene apparently exists as a single copy in the tachyzoite haploid genome of the three strains of T. gondii examined. Northern blot analyses revealed that the cDNAs hybridize with a major T. gondii RNA species of 1.1 kb. Together the cDNAs encompass 1051 bp of cDNA sequence containing an open reading frame with the capacity to encode a 28 kDa protein. Antibodies that were affinity purified using recombinant fusion proteins produced by two of the clones reacted on protein blots of whole T. gondii lysate with a single antigen having an apparent molecular mass of 28 kDa. Both recombinant fusion proteins reacted with IgG antibodies in sera of mice and humans infected with T. gondii and therefore might be useful for the development of diagnostic assays for T. gondii infection.

Amino Acid Sequence↗
PubMed1989

Morphine-like activity of substituted amides & imides of [D-Ala2, Met5]-enkephalin.

Six enkephalin analogues (N-substituted amides and imides of [D-Ala2, Met5]-enkephalin) were synthesized and tested for opioid activity. All the compounds, except one i.e., compound IV, showed analgesic activity which was much higher than Met-enkephalin and morphine in mice and inhibited electrically induced contractions of isolated guineapig ileum, [D-Ala2, Met5]-enkephalin-morpholide and [D-Ala2, Met5]-enkephalin-beta-Ala-amide were the most potent analgesics and nearly 6 and 500 times as active as morphine and Met-enkephalin respectively. Both the compounds were equipotent on the guineapig ileum preparation, whereas the beta-Ala-amide was about twice as active as the morpholide in the electrically stimulated mouse vas deferens preparation.

Amides↗
PubMed1987

Protective immunity in toxoplasmosis: correlation between antibody response, brain cyst formation, T-cell activation, and survival in normal and B-cell-deficient mice bearing the H-2k haplotype.

Correlations of Toxoplasma gondii-specific immunoglobulin M (IgM) and IgG production, antigen-specific T-cell activation, and the number of brain cysts were compared in immunocompetent CBA/J (H-2k), C3H/He (H-2k), and B-cell-deficient CBA/N (H-2k) mice. Almost all of the C3H/He mice (94%) survived in comparison to CBA/J (71%) and CBA/N (53%) mice following infection with 20 cysts of Me 49, an avirulent strain of T. gondii. The mortality in susceptible mice was reduced by treatment of the animals with sulfadiazine during the acute stage of infection. Decreased mortality in CBA/J and C3H/He mice as well as in B-cell-deficient mice was paralleled by formation of fewer brain cysts. The Toxoplasma-specific T-cell proliferation was markedly enhanced in all three strains at day 15 postinfection but not at day 45 postinfection when compared to animals not treated with the drug. In contrast, Toxoplasma-specific IgM and IgG levels were lower in CBA/J and CBA/N mice treated with sulfadiazine than in untreated mice of these strains. Although CBA/N mice developed almost no humoral response either with or without drug treatment, they produced fewer brain cysts than normal CBA/J mice. The results indicate a major role of cell-mediated immunity in protection against an acute Toxoplasma infection.

Animals↗
PubMed1987

Ultrastructural localization of an intracellular Toxoplasma protein that induces protection in mice.

We report the ultrastructural localization of Toxoplasma antigens recognized by monoclonal antibody F3G3, which protects mice against lethal challenge. By using colloidal immunogold labeling, F3G3 failed to react with the surface of intact Toxoplasma cells, confirming previous observations that it recognizes an intracellular antigen. Immunoperoxidase labeling with F3G3 was obtained only when Toxoplasma cells were previously exposed to Triton X-100. A specific immunoperoxidase reaction was located beneath the surface membrane in the region of the pellicle and within the elaborate network of vesicles which are extruded from the surface of Toxoplasma cells during entry into host cells. Similar results were obtained with mouse polyclonal sera and a second monoclonal antibody, 6-86-1E11, both of which were produced against the F3G3 affinity-purified protein. The location of the epitope recognized by F3G3 was confirmed by purifying T. gondii-derived surface membrane vesicles, separating these proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and immunoblotting. Monoclonal antibody 6-86-1E11 and the analogous polyclonal sera reacted with the antigenically related proteins of 58 and 28 kilodaltons that were found both in the intact organisms and in the purified surface membrane vesicles. These results indicate that the epitope recognized by F3G3 is located beneath the Toxoplasma cell surface membrane and is contained within plasma membrane-derived vesicles.

Animals↗
PubMed1986

Different regulation of the L3T4-T cell subset by B cells in different mouse strains bearing the H-2k haplotype.

Splenic L3T4-T cells from Toxoplasma gondii-infected CBA/J (H-2k, Igh 1a) but not C3H/He (H-2k, Igh 1j) mice responded with marked antigen-specific proliferation and interleukin 2 (IL 2) production, as well as concanavalin A-induced proliferation. The proliferative response of C3H/He spleen cells could be restored in part in vitro by addition of exogenous recombinant IL 2. The observed unresponsiveness of C3H/He spleen cells was due to the release of IL 2-inhibiting factors. These factors, present in culture supernatants from antigen restimulated C3H/He spleen cells, blocked the growth of an IL 2-dependent T cell line in the presence of optimal concentration of IL 2. During the early stages of infection, C3H/He splenic macrophages lacked the capacity to present antigen. In addition a nonspecific B cell-mediated suppression of T cell proliferation was observed. In later stages of infection macrophages displayed normal antigen-presenting function in comparison with macrophages of normal uninfected mice. At this stage of infection nonspecific, minor histocompatibility restricted B cell suppression was observed. These results suggest a possible role of B cells in regulation of T cell immunity to T. gondii.

Animals↗
PubMed1986

Oxygen-independent killing by alveolar macrophages.

We have found that normal alveolar macrophages can kill an intracellular parasite by a mechanism that does not involve toxic metabolites of oxygen. We studied the interaction between Toxoplasma gondii and rat alveolar macrophages in vitro. We were interested in Toxoplasma because it causes pneumonia in immunosuppressed patients but not in healthy individuals, and we chose the rat because it resembles immunocompetent human subjects in being resistant to T. gondii. Resident rat alveolar macrophages could kill large numbers of T. gondii. This occurred without a respiratory burst as judged by intracellular reduction of nitroblue tetrazolium and quantitative release of superoxide. Furthermore, scavengers of toxic oxygen metabolites had no effect on the toxoplasmacidal activity of the alveolar macrophages, nor did prior exhaustion of their respiratory burst with PMA. Whereas acid pH (e.g., 4.5-6.0) rapidly kills extracellular T. gondii, raising of the intralysosomal acid pH of rat alveolar macrophages by incubating them with weak bases did not inhibit their ability to kill T. gondii. Killing of Toxoplasma occurred within 1 h of initial exposure to the alveolar macrophages. However, there was no evidence that killing preceded ingestion; Toxoplasma attached to the surface of the cell appeared viable, and when phagocytosis was blocked with sodium fluoride the organisms survived. These results indicate that rat alveolar macrophages possess a powerful nonoxidative microbicidal mechanism, which is distinct from acidification of the phagolysosome but which probably involves phagosome formation. This mechanism may be clinically relevant, for we have recently observed that human alveolar macrophages also kill T. gondii by an oxygen-independent process.

Ammonium Chloride↗
PubMed1986

Antibodies to immune response gene products inhibit the IgM and IgG antibody response but not the development of resistance to Toxoplasma gondii.

We have examined the effects of a monoclonal antibody directed against immune response gene products on the appearance of antibodies and development of resistance to Toxoplasma gondii. In vivo administration of a single dose of anti-I-Ak antibody to C3H/He (H-2k) and not BALB/c (H-2d) mice suppressed both the IgM and IgG response to two different strains of Toxoplasma. Administration of anti-I-Ak antibody to mice 5 days before and 10 days after infection resulted in complete inhibition of IgM and a more pronounced inhibition of IgG response to Toxoplasma. Under these experimental conditions, development of resistance against a subsequent challenge with a virulent strain of Toxoplasma was not affected. The microbicidal and tumoricidal activities of macrophages obtained from anti-I-Ak-treated, Toxoplasma-infected mice and mice infected with Toxoplasma alone were equivalent. Mice treated with anti-I-Ak antibody demonstrated a decreased proliferative response to lipopolysaccharide, a B-cell mitogen. Enumeration of B-cell numbers in anti-I-Ak-treated mice revealed a pronounced decrease in B-cell counts.

Animals↗
PubMed1986

Traditional concepts of mental disorder among Indian psychiatric patients: preliminary report of work in progress.

In a medically pluralistic setting a range of health care providers offer not only different forms of treatment, but different ways of understanding illness. Even within a single tradition, these concepts evolve over time. Chapters in the classical texts of Ayurveda describe varieties of severe mental disorder (unmada) arising from a particular humoral imbalance (dosa) or arising in association with specific demons and deities (bhuta) that produce distinct character changes and symptom patterns. Patients currently presenting for treatment of mental disorder may describe their illness with reference to these concepts, but they also rely on other indigenous traditional concepts such as astrology, karma, the effects of other humoral relationships, such as semen loss and so forth; or they may rely on ideas derived from cosmopolitan medicine or both. Patients presenting to allopathic psychiatric centers in India were studied to determine whether patterns of help seeking could be predicted from the conceptual model by which they understood their illness. We elicited explanatory models from patients and obtained a history of prior consultations to other types of healer. Preliminary findings were notable for the pervasiveness of prior use of folk healers and the prominence of somatic symptoms among patients presenting to these allopathic physicians. Hypotheses regarding the impact of explanatory models on patterns of medical help seeking require further study from a larger and more diverse data base.

Attitude to Health↗
PubMed1985

Cell free synthesis of Toxoplasma gondii antigens.

Functionally active poly(A)-containing mRNA was isolated from tachyzoites of the RH strain of Toxoplasma gondii. The T. gondii mRNA was capable of directing the synthesis of proteins in a wheat germ in vitro translation system, but not in a cell free system derived from rabbit reticulocyte lysate. Efficient translation in the wheat germ system required spermine and exogenous tRNA. Amino acid incorporation was maximal at 110 mM K+ and 1.8 mM Mg2+. Tachyzoite antigens synthesized in vitro were immunoprecipitated with T. gondii antibodies from rabbits, mice and humans. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of immunoprecipitated polypeptides yielded patterns that differed according to antibody source, but all T. gondii antibody preparations reacted with a translation product with an apparent molecular weight of 24 000.

Animals↗