IN VIVO PEPTIDES POSITIVELY SELECT AND FINE-TUNE T CELLS

The affinity for TCR interactions with self-peptide/MHC complexes (pMHC) in the thymus critically affects immature thymocytes that newly express TCRs. Previous fetal thymus organ culture experiments have indicated that difference in the affinity for thymic TCR/pMHC interactions not only determines thymocyte fate between positive and negative selection, but also affects Ag responsiveness of positively selected thymocytes. In the current study, we examined whether TCR/pMHC affinity during positive selection in the thymus would further affect Ag responsiveness of mature T cells in the periphery. To do so, OVA peptide variants were in vivo administered to TAP1-deficient OT-I/TCR-transgenic mice in which T cell development was otherwise arrested at CD4+CD8+ thymocytes because of the lack of self-pMHC presentation in thymic APCs. We found that a group of peptide variants induced the transient generation of OT-I CD8+ T cells in the thymus and the periphery. We also noticed that the affinity threshold for positive and negative selection detected in adult mice in vivo was higher than that measured in fetal thymus organ culture experiments in vitro. Interestingly, we further found that the affinity for positively selecting peptides proportionally affected TCR responsiveness of peripheral naive CD8+ T cells. These results indicate that in vivo administration of a peptide can promote T cell selection in the thymus and the affinity for TCR/pMHC interaction during positive selection fine-tunes Ag responsiveness of peripheral T cells

Determination of pond water quality for aquaculture and ecosystem management

Fish is the main source of animal protein for the common people of Bangladesh. About 37% of the inland fishes are obtained from the closed water fish culture where ponds play vital roles in the production system. The present study was carried out to determine the water quality (physico-chemical and biological factors) of five uncultivated or under cultivated ponds in the Chittagong University campus, Bangladesh, for aquaculture and ecosystem management. Temperature, pH, EC, BOD, COD, TSS, turbidity, NO2-, PO4 -, free CO2, CO3 -, HCO3-, Cl-, total viable bacterial count and total coliform were determined. Isolation and identification of Escherichia coli and Salmonella sp. from the water samples were performed to investigate the antibiotic sensitivity. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against ciprofloxacin was also investigated. The findings reveal that there was no significant difference in temperature (19°C to 20°C), pH (6.7 to 7.4), electrical conductivity and Cl- values in the water among the ponds and that was within the range of the requirements for the fish cultivation. Both turbidity and total dissolved solids was highest in the uncultivated botanical garden pond 2 (BGP2). BOD, COD, NO2- , PO 4-2, HCO3-, and free CO2 concentration was beyond the permissible limits for aquaculture. Total viable count and total coliform ranged from 1.3 × 10 4 to 6.6 × 10 5 cfu ml-1 and from 0.0205×10 2 to 1.10×10 2 ml-1 respectively, among the ponds where both these parameters were highest in the naturally polluted BGP2. Most of the isolated E. coli and Salmonella sp. were sensitive but few showed resistance against the antibiotics, especially in BGP1, where fishes were cultivated commercially