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Biomedical subjects

B Saha

Publications and source records attributed to B Saha.

69 records · Page 4Linked to original sources
PubMed1996

Electron microscopic characteristics of actinomycetic agents having aetiological association with human leprosy and epizootic ulcerative syndrome of fish.

The transmission electron microscopic (TEM) studies of the human leprosy derived chemoautotrophic nocardio-form (CAN) bacteria and EUS derived CAN bacteria showed presence of double contoured cell-walls consisting of an electron transparent and a dense layer. The fibrillar structures on the surface of these CAN bacterial cells also suggested their similarity to the human tissue derived Mycobacterium leprae cells. These EM studies further revealed mycelial and coccoid bodies in all these bacteria as was observed originally.

Actinomycetales↗
PubMed1995

Macrophage-T cell interaction in experimental visceral leishmaniasis: failure to express costimulatory molecules on Leishmania-infected macrophages and its implication in the suppression of cell-mediated immunity.

The most important immunopathological consequence of infection with Leishmania seen in murine and human hosts is the suppression of T cell-mediated immune responses to both mitogens and leishmanial antigens. It has been suggested that this suppression is mediated by macrophages, either by defective antigen processing and presentation or by the elaboration of suppressive mediators like prostaglandins. Optimum activation of T helper cells requires not only T cell receptor occupancy by the antigen-Ia complex, but also costimulatory signals provided by the antigen-presenting cells. We investigated the status of several costimulatory molecules on infected macrophages from both genetically susceptible BALB/c and resistant C57BL/6 mice. Our results demonstrate that upon parasitization, the macrophages become unable to deliver costimulatory signals to T helper cells, and that this effects is mediated by prostaglandins, as the inhibition of its synthesis by indomethacin recovered the defect. Upon infection with L. donovani, B7-1 expression was decreased, while ICAM-1 was marginally increased in BALB/c macrophages and there was no significant change in the expression of B7-1 and ICAM-1 in Leishmania-infected C57BL/6 macrophages. Expression of VCAM-1 did not change during infection. This selective alteration in the expression of costimulatory molecules on L. donovani-infected BALB/c macrophages was caused by the living parasite, as shown by the fact that killing of the parasites by stibogluconate led to no alteration in the levels of costimulatory molecules. We found that the change in B7-1 expression on the surface of infected macrophages resulted in the inhibition of delayed-type hypersensitivity-mediating functions of T helper cells from BALB/c mice. The results described in this study not only throw light on the possible mechanism of leishmanial pathogenesis, but also open up the possibility of immunotherapy of leishmaniasis by selective manipulation of costimulatory molecules.

Animals↗
PubMed1995

Immunobiological studies on experimental visceral leishmaniasis. IV. Kinetics of evolution of disease-promoting versus host-protective cells of monocyte-macrophage lineage and their characterization.

The evolution of cells of the monocyte-macrophage lineage (MML cells) in the spleen of Leishmania donovani (LD) infected BALB/c mice was studied. Spleen cells were fractionated on a discontinuous percoll gradient and adherent cells (AC) were purified from fractionated spleen cells by adherence steps that appeared at the interfaces of 25-35%, 35-40%, 40-45% and 45-50% percoll gradients. The AC were characterized as MML cells on the basis of positive staining for non-specific esterase. Adherent cells that appeared at the interfaces of 25-35% and 40-45% were defined as A and C, respectively, and both of them showed extreme variation in a progressive infection. It was observed that A supported parasite replication whereas C remained refractory when infected with LD in vitro. Furthermore, when A cells and C cells were used as antigen-presenting cells to stimulate mixed population of IFN-gamma producing and IL-4 producing T-cells, it was observed that IL-4 and IFN-gamma were the predominating cytokine in the T-cell supernatant, respectively. Both A and C were found to be increased hand-in-hand up to 5 months of infection and from then on A decreased and C increased in their numerical strength (A-C reciprocity). The evolution of A-C reciprocity coincided with the gradual reduction in the parasitaemia in the spleen suggesting that this may contribute to the acquisition of anti-leishmania immunity.

Animals↗
PubMed1994

Macrophage-T cell interaction in experimental mycobacterial infection. Selective regulation of co-stimulatory molecules on Mycobacterium-infected macrophages and its implication in the suppression of cell-mediated immune response.

The most important immunopathological consequence of experimental mycobacterial infection is the suppression of T cell-mediated immune response to both mitogens and mycobacterial antigens. We registered that there was decreased concanavalin A-induced spleen cell proliferation in infected susceptible BALB/c mice as compared to normal mice. In resistant (C3H/HeJ) mice, infection with the bacteria did not induce any suppression in the mitogen-induced lymphoproliferation. Likewise, delayed-type hypersensitivity (DTH) responses, to keyhole limpet hemocyanin and mycobacterial crude soluble antigen were suppressed in infected BALB/c mice but not in C3H/HeJ mice. This depressed T helper cell function may either be due to defective T cell-receptor occupancy by antigen-Ia complex or altered co-stimulatory signals provided by antigen-presenting cells. In the present study, we have investigated the status of certain co-stimulatory molecules on the infected macrophages from both susceptible and resistant mice. Our results demonstrate that upon mycobacterial infection, the macrophages are rendered incapable of delivering the co-stimulatory signals to T helper cells, possibly due to the involvement of prostaglandin, as inhibition of its biosynthesis by indomethacin reversed the defect. Furthermore, the selective regulation was bacteria-induced as killing of the bacteria by rifampicin abrogated the derangements in the expression of co-stimulatory molecules on the Mycobacterium-infected macrophages. Our observations revealed that upon infection with Mycobacterium tuberculosis, B7 was down-regulated while ICAM-1 was increased only in BALB/c but not in C3H/HeJ mice. Expression of VCAM-1 did not change during the infection in either strain of mice. We found that these changes in ICAM-1 and B7 expression on the surface of infected macrophages resulted in inhibition of DTH-mediating functions of T helper cells from BALB/c mice. The results obtained in this study describe not only a novel immune evasion strategy adopted by Mycobacterium, but also open up the possibility of immunotherapy of mycobacterial infection by selective manipulation of co-stimulatory molecules.

Animals↗
PubMed1994

An eight-year field trial on antileprosy vaccines among high-risk household contacts in the Calcutta metropolis.

One-hundred-seventy-nine lepromin-negative household contacts were vaccinated with heat-killed Mycobacterium leprae, BCG, or a combination of the two. Vaccination induced lepromin positivity in 131 of these contacts. Over an 8-year follow-up period, 12 lepromin-positive contacts developed leprosy, all tuberculoid; while 2 lepromin-negative vaccinated contacts developed leprosy, both lepromatous. Overall, 7.8% of the vaccinated contacts developed the disease. Seven-hundred-fourteen household contacts were not vaccinated, and served as controls. Among the 504 who were lepromin positive, leprosy developed in 35, all tuberculoid, over the 8-year follow up. Among the 210 lepromin-negative unvaccinated contacts, 61 developed leprosy: tuberculoid in 29, borderline in 4, lepromatous in 8, and indeterminate in 20. Overall, 13.5% of the 714 unvaccinated contacts and 29.0% of the 210 unvaccinated, lepromin-negative contacts developed leprosy. Vaccination could not induce lepromin positivity in all contacts. The three vaccines were equally effective in inducing lepromin positivity. Vaccination reduced the overall incidence of leprosy from 13.5% to 7.8% among household contacts but did not reduce the incidence of lepromatous leprosy (1.2% of all the vaccinated and 1.1% of all the unvaccinated contacts).

BCG Vaccine↗
PubMed1993

Allelic loss on chromosome 17 in human ovarian cancer.

In order to identify a common region of deletion on chromosome 17 potentially containing a tumor-suppressor gene, 27 ovarian carcinomas and 3 ovarian tumors of low malignant potential (LMP) were examined for loss of heterozygosity (LOH) at 6 p arm and 10 q arm loci. Ninety percent of all tumors had deletions at one or more loci. On the p arm, there was a single near-common region of deletion on 17p13.3 (D17S30/pYNZ22.1; 86% LOH), an intervening locus with a low LOH rate, and a more proximal locus on 17p11.2 (D17S58/pEW301; 82% LOH) with a high LOH rate. In less aggressive tumors, LOH at D17S30 was not accompanied by LOH at p53. The q arm had a common region of deletion for high-stage carcinoma at D17S579 (Mfd188; 74% LOH) on q21, a locus tightly linked to the familial breast-ovarian-cancer syndrome (BRCAI) locus. D17S579 was lost in all informative high-stage carcinomas and retained in all low-stage carcinomas and tumors of LMP. There may be at least 2 tumor-suppressor genes, an early-acting gene on the p arm and a gene on the q arm involved in tumor progression and metastasis.

Adult↗
PubMed1993

Immunobiological studies on experimental visceral leishmaniasis. III. Cytokine-mediated regulation of parasite replication.

The role of T-cell-derived cytokines in the regulation of Leishmania donovani replication was studied in a murine model. It was observed that in H-2d mice at the early and later stages of the disease IFN-gamma-secreting T cells predominate, whereas in between the above stages IL-4-secreting T cells predominate. Possibly, IL-4 abrogates the protective ability of IFN-gamma and thereby exponential parasite growth is ensured at the active stage of the disease. By contrast, H-2b mice were possibly incapable of inducing IL-4-secreting T cells and therefore parasite replication remains under control at any point post infection.

Animals↗
PubMed1992

Immunobiological studies on experimental visceral leishmaniasis. II. Adherent cell-mediated down-regulation of delayed-type hypersensitivity response and up-regulation of B cell activation.

Visceral leishmaniasis or kala-azar is characterized by a variety of immunopathological consequences in man. The most remarkable of these are the depression of cell-mediated immunity and polyclonal B cell activation. The consequences observed in man could be induced in a murine model by inoculating the causative agent, Leishmania donovani. The cell-mediated response was studied in this murine model in terms of the delayed-type hypersensitivity (DTH) response toward leishmania antigen in a progressive infection. BALB/b (H-2b) mice showed progressive enhancement in the DTH response, whereas BALB/c (H-2d) mice showed strong DTH at the onset which gradually disappeared (defined as DTH-negative phase) and reappeared again at the later stage of infection. Adoptive transfer of enriched populations of splenic T cells from infected BALB/c mice together with parasite antigen into the footpad of syngenic normal recipients produced a dramatic enhancement in the DTH response, except at the onset of the DTH-negative phase. These observations indicate that adherent cells have a role in suppression of the cell-mediated immune response and also that another mechanism operates at the onset of the DTH-negative phase. This DTH-negative phase was not caused by depletion of DTH-mediating cells from the repertoire, but rather by suppression mediated by a subset of T cell evolved in the course of infection. Characterization on the basis of lymphokine production of the T cells mediating the DTH response and of T cells mediating suppression of the DTH response showed them to be of Th1 and Th2 type, respectively. Studies also indicated that at the onset and the later stages of infection suppression was mediated by adherent cells, but at the onset of DTH-negative phase, in particular, suppression was mediated by Th2 cells. Furthermore, experiments also showed that adherent cells from infected mice gained another property, that of driving B cells, in a T cell-dependent manner.

Animals↗
PubMed1991

Immunobiological studies on experimental visceral leishmaniasis. I. Changes in lymphoid organs and their possible role in pathogenesis.

Studies were carried out to determine changes in lymphoid organs i.e. spleen, lymph node and bone marrow (BM) in progressive experimental visceral leishmaniasis. Mononuclear phagocytes in the BM were increased; spleens showed a hypercellularity coupled with a rise in parasite burden while secondary follicles with no apparent depletion of paracortex were seen in the lymph node. This enhanced proliferation of mononuclear phagocytes in the BM and probably their subsequent recruitment in the spleen could be induced in naive recipients by injecting nylon wool-purified lymph node cells derived from infected mice together with sonicated leishmanial antigen(s). Similar changes could also be induced in the BM of naive recipients by injecting serum of infected mice. In control experiments where both donor and recipients were uninfected such changes were not apparent. A working hypothesis is proposed to delineate the role of lymphoid organs in the pathogenesis of experimental visceral leishmaniasis.

Animals↗
PubMed1991

Development of a highly sensitive enzyme linked immunosorbent assay for human serum progesterone using penicillinase.

A simple, highly sensitive, heterologous, competitive, penicillinase based tube ELISA for human serum progesterone has been developed. Specific antisera against progesterone was raised in rabbits using 11 alpha - hydroxyprogesterone hemisuccinate-BSA. Progesterone-3-CMO was coupled to penicillinase by the carbodiimide method. The standard curve covered a wide range from 5 pg/tube to 800 pg/tube. The sensitivity of the assay was 3.8 pg/tube. The intrassay coefficient of variation ranged from 8.6% to 11.2% at low concentration while at medium and high concentrations it ranged from 5.3% to 8.9%. The interassay coefficient of variation for the low, medium and high concentrations of progesterone were 9.6%, 10.7% and 6.5% respectively. Parallelism between the standard curve and the sample dilution curve indicated accuracy of the assay. Samples measured by RIA and ELISA showed an excellent correlation (r = 0.98).

Antibodies↗
PubMed1989

A new method of plasmid DNA preparation by sucrose-mediated detergent lysis from Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive).

A simple and cheap method of plasmid DNA preparation from both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) organism is presented here. In this method, in place of the high-priced chemicals lysostaphin and lysozyme which are commonly used for removal of cell-wall during plasmid DNA preparation from gram-positive and gram-negative bacteria, respectively, only sucrose has been used. Firstly, bacteria is treated with Trizma (pH 8.0) containing 100% sucrose (hypertonic solution). Due to this osmotic shock, protoplasm covered by the plasma membrane of bacteria possibly shrinks and becomes detached from the cell-wall. Osmotically sensitive cells thus formed, from gram-positive (S. aureus) and gram-negative (E. coli) bacteria, are finally lysed by the lysis mixture, containing brij 58 and sodium deoxycholate. The lysate is centrifuged at 15,000 rpm for 30 min to pellet the cell debris. The supernatant containing plasmid DNA is treated with either polyethylene glycol or isopropanol. The precipitate which contains plasmid DNA is dissolved in a buffer containing Tris, EDTA, NaCl, and sodium dodecyl sulfate (pH 8.0); thus protein is denatured and removed. Finally, RNA is removed by RNase treatment. The average yield of staphylococcal plasmid DNA as well as plasmid pBR322 from E. coli HB101 in 100% sucrose-treated preparations is greater than that of lysostaphin- and lysozyme-treated preparations. This method is applicable for both large-scale and small-scale preparations. The substrate activity for restriction enzyme, cloning, transforming ability, and electron microscopic profile of the plasmid DNA prepared by this method remains unaltered.

Cell Wall↗
PubMedDate not supplied

Role of paucibacillary leprosy in the transmission of disease.

The objective of this study was to establish that paucibacillary leprosy also carried increased risk of infection to the community. All members of 100 families with an index paucibacillary case were clinically, bacteriologically and immunologically examined. The "comparison" group was sampled from suspect register. Fifty-six cases occurred among 944 contacts of index paucibacillary cases; of these, four were multibacillary and 52 were paucibacillary. In the "comparison" group, two contacts out of 760 developed paucibacillary leprosy. This difference, between the two groups, was statistically significant. All the 56 cases in the index case families were under 20 years of age; and 50 of them were aged under 15 years. Male/female ratio was 2.1:1. Of the 56 cases, 28 shared the same bed with the index patient, 20 shared the same room and eight lived in the same house. Lepromin positivity rate was higher in "comparison" families (92.2%) than in index case families (74.6%), the difference being statistically significant (x = 6.09, P < 0.001). Contacts of index case families, therefore, were immunologically at higher risk than contacts of "comparison" families.

Adolescent↗