Localization of class i histocompatibility molecule assembly by subfractionation of the early secretory pathway

Class I molecules of the major histocompatibility complex bind peptides derived from cytosolic proteins and display them on the cell surface. This function alerts cytotoxic T cells to the presence of intracellular pathogens. Class I molecule assembly requires the association of the heavy chain with β₂-microglobulin, accompanied by peptide loading via specific transporters. This study localizes where these assembly steps take place, using monoclonal antibodies recognizing class I molecules in different assembly states to analyze subcellular fractions of the early secretory pathway. The distribution of peptide-loaded class I molecules was more localized than the distribution of the total pool of class I molecules in the early secretory pathway. Loaded molecules colocalized with the peptide transporter, free heavy chains, and the chaperone calnexin in high density rough endoplasmic reticulum (RER) membranes. These data suggest that subunit assembly and peptide acquisition occur at the same intracellular site. Class I molecules also localized to less dense subfractions of the early secretory pathway, which contained comparatively less peptide-loaded molecules than the high density RER fractions, at steady state. Following a 15 °C temperature block, class I molecules accumulated in these less dense membrane fractions, indicating that these fractions represent the intermediate compartment where empty class I molecules are trapped in mutant cells. In the presence of cycloheximide, a pool of class I molecules recycling to the RER was detected, suggesting empty molecules recycle to acquire peptide.     

The haemotoxicity of mitomycin in a repeat dose study in the female CD-1 mouse

Mitomycin (MMC), like many antineoplastic drugs, induces a predictable, dose-related, bone marrow depression in man and laboratory animals; this change is generally reversible. However, there is evidence that MMC may also cause a late-stage or residual bone marrow injury. The present study in female CD-1 mice investigated the haematological and bone marrow changes induced by MMC in a repeat dose study lasting 50 days. Control and MMC-treated mice were dosed intraperitoneally on eight occasions over 18 days with vehicle, or MMC at 2.5 mg/kg, autopsied (n = 6-12) at 1, 7, 14, 28, 42 and 50 days after the final dose and haematological changes investigated. Femoral nucleated bone marrow cell counts and levels of apoptosis were also evaluated and clonogenic assays carried out; serum levels of FLT3 ligand (FL) were assessed. At day 1 post-dosing, MMC induced significant reductions in RBC, Hb and haematocrit (HCT) values, and there were decreases in reticulocyte, platelet, and femoral nucleated cell counts (FNCC); neutrophil, lymphocyte and monocyte values were also significantly reduced. On days 7 and 14 post-dosing, all haematological parameters showed evidence of a return towards normal values, but at these times, and at day 28, values for RBC and FNCC remained significantly reduced in comparison with controls. At days 42 and 50 post-dosing, many haematological parameters in MMC-treated mice had returned to control levels; however, there remained evidence of late-stage effects on RBC, Hb and HCT values, and FNCC also continued to be significantly decreased. Results for granulocyte-macrophage colony-forming units and erythroid colonies showed a profound decrease immediately post-dosing, but a return to normal values was evident at day 50. Serum FL concentrations demonstrated very significant increases in the immediate post-dosing period, but a return to normal was seen at day 50 post-dosing; a relatively similar pattern was seen in the number of apoptotic femoral marrow nucleated cells. The histopathological examination of kidney tissues from MMC animals at day 42 and 50 post-dosing showed evidence of hydronephrosis with cortical glomerular/tubular atrophy and degeneration. It is therefore concluded that MMC administered on eight occasions over 18 days to female CD-1 mice at 2.5 mg/kg induced profound changes in haematological and bone marrow parameters in the immediate post-dosing period with a return to normal levels at day 50 post-dosing; however, there was evidence of mild but significant late-stage/residual effects on RBC and FNCC, and on cells of the erythroid lineage in the bone marrow.     

Complex consultations and the ‘edge of chaos’

Complexity theory has attracted considerable attention in recent years, both within medicine and in the wider world. Its themes of uncertainty and non-linearity resonate deeply with the experience of working in general practice. Describing the consultation as a complex, adaptive system provides a coherent theoretical basis for understanding the consultation, which has so far been lacking. Understanding the consultation as a complex, adaptive system offers insights into the consultation of that may prove to be of practical use to clinicians.     

At Least Four Percent of the Salmonella typhimurium Genome Is Required for Fatal Infection of Mice

Salmonella typhimurium infection of mice is an established model system for studying typhoid fever in humans. Using this model, we identified S. typhimurium genes which are absolutely required to cause fatal murine infection by testing independently derived transposon insertion mutants for loss of virulence in vivo. Of the 330 mutants tested intraperitoneally and the 197 mutants tested intragastrically, 12 mutants with 50% lethal doses greater than 1,000 times that of the parental strain were identified. These attenuated mutants were characterized by in vitro assays which correlate with known virulence functions. In addition, the corresponding transposon insertions were mapped within the S. typhimurium genome and the nucleotide sequence of the transposon-flanking DNA was obtained. Salmonella spp. and related bacteria were probed with flanking DNA for the presence of these genes. All 12 attenuated mutants had insertions in known genes, although the attenuating effects of only two of these were previously described. Furthermore, the proportion of attenuated mutants obtained in this study suggests that mutations in about 4% of the Salmonella genome lead to 1,000-fold or greater attenuation in the mouse typhoid model of infection. Most of these genes appear to be required during the early stages of a natural infection.     

Mapping the architecture of the ATP-binding site of the KATP channel subunit Kir6.2

ATP-sensitive potassium (K_ATP) channels comprise Kir6.2 and SUR subunits. The site at which ATP binds to mediate K_ATP channel inhibition lies on Kir6.2, but the potency of block is enhanced by coexpression with SUR1. To assess the structure of the ATP-binding site on Kir6.2, we used a range of adenine nucleotides as molecular measuring sticks to map the internal dimensions of the binding site. We compared their efficacy on Kir6.2–SUR1, and on a truncated Kir6.2 (Kir6.2ΔC) that expresses in the absence of SUR. We show here that SUR1 modifies the ATP-binding pocket of Kir6.2, by increasing the width of the groove that binds the phosphate tail of ATP, without changing the length of the groove, and by enhancing interaction with the adenine ring.     

Outbreak of serogroup C meningococcal disease caused by a variant of Neisseria meningitidis serotype 2a ET-15 in a community of men who have sex with men

We describe an outbreak, in a community of men who have sex with men, of serogroup C meningococcal disease caused by a genetic variant of the serotype 2a ET-15 Neisseria meningitidis characterized by a point mutation in the gene coding for the serotype 2a antigen. A microbiological characterization of the outbreak strain is presented in this report.     

Diarrhea Associated with Vibrio fluvialis in the United States

We report the isolation in the United States of Vibrio fluvialis from the stools of a patient who had severe watery diarrhea without fever and who subsequently died. V. fluvialis, a known enteric pathogen in other parts of the world, should be suspected in patients with watery diarrhea, especially in coastal areas.