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Biomedical subjects

C A Klein

Publications and source records attributed to C A Klein.

At least 37 records · Page 2Linked to original sources
PubMed1994

The p2 domain of human immunodeficiency virus type 1 Gag regulates sequential proteolytic processing and is required to produce fully infectious virions.

The proteolytic processing sites of the human immunodeficiency virus type 1 (HIV-1) Gag precursor are cleaved in a sequential manner by the viral protease. We investigated the factors that regulate sequential processing. When full-length Gag protein was digested with recombinant HIV-1 protease in vitro, four of the five major processing sites in Gag were cleaved at rates that differ by as much as 400-fold. Three of these four processing sites were cleaved independently of the others. The CA/p2 site, however, was cleaved approximately 20-fold faster when the adjacent downstream p2/NC site was blocked from cleavage or when the p2 domain of Gag was deleted. These results suggest that the presence of a C-terminal p2 tail on processing intermediates slows cleavage at the upstream CA/p2 site. We also found that lower pH selectively accelerated cleavage of the CA/p2 processing site in the full-length precursor and as a peptide primarily by a sequence-based mechanism rather than by a change in protein conformation. Deletion of the p2 domain of Gag results in released virions that are less infectious despite the presence of the processed final products of Gag. These findings suggest that the p2 domain of HIV-1 Gag regulates the rate of cleavage at the CA/p2 processing site during sequential processing in vitro and in infected cells and that p2 may function in the proper assembly of virions.

Amino Acid Sequence↗
PubMed1993

TNF-alpha and cyclooxygenase metabolites do not modulate C. albicans septic shock with disseminated candidiasis.

We analyzed differences in host regulation of tumor necrosis factor-alpha (TNF-alpha) production and pathophysiological responses in conscious rats after infection with two strains of pathogenic Candida albicans spp. (CA-1 and CA-2) compared with Escherichia coli serotype 055:B5 (EC). The hypothesis was tested that, in contrast to EC, hypotension, organ injury, and mortality after candidemia are not obligatorily dependent on TNF-alpha or TNF-alpha-induced cyclooxygenase pathway metabolites. Dose, viability, and strain-specific dependencies were established after intravenous 10(6) or 10(9) viable CA, as well as heat-killed (HK) or Formalin-inactivated (FI) CA blastospores, compared with live EC at the 24-h LD25 [10(9) colony-forming units (CFU)] and LD100 (10(10) CFU). Shock without endotoxemia developed 4-8 h after 10(9) live CA-1 or CA-2 (LD100 at 24 h) with disseminated yeast-mycelial transformation and increased microvascular permeability in multiple organs but not after HK or FI CA-1. Peak serum TNF-alpha after an LD100 of CA-1 or CA-2 was < 3% of LD25 EC values and was < 1% of peak values during lethal bacteremia. Similar pathogen-specific differences were found in liver- and lung-associated TNF. Production of functionally inactive TNF-alpha during candidemia was excluded by enzyme-linked immunosorbent assay and sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Western blotting. Passive immunization against TNF-alpha 2 h before microbial challenge was not protective against CA but prevented otherwise lethal EC sepsis. Cyclooxygenase inhibition also failed to attenuate candidemic shock. We conclude that the magnitude and kinetics of TNF-alpha production and TNF-alpha-dependent immunophysiological responses are differentially regulated after lethal fungal vs. gram-negative bacterial infection. Thus TNF-alpha is not a pivotal mediator of the acute Candida septic shock syndrome with disseminated candidiasis.

Animals↗
PubMed1992

Differential systemic and intrapulmonary TNF-alpha production in Candida sepsis during immunosuppression.

Candida albicans (CA) increasingly causes septic shock, acute lung injury, and multiple organ damage during immunosuppression-related neutropenia. However, the effects of neutrophil (PMN) depletion on induction of tumor necrosis factor-alpha (TNF) by CA and its potential mediation of Candida septic shock are unknown. We hypothesized that reduced CA uptake by circulating PMNs during cyclophosphamide (CY)-related neutropenia sensitizes to TNF-mediated shock from enhanced cytokine production after phagocytosis by tissue macrophages. Absolute or relative neutropenia (PMNs < or = 500/microliters or 2,500/microliters) was modeled in rats by intraperitoneal CY 4-8 days before 10(9) yeast-phase CA (acute studies < or = 24 h, n = 81 animals) or 10(6) CA (subacute studies < or = 72 h, n = 25). Compared with neutrophil-sufficient rats, absolute neutropenia accelerated hemodynamic collapse and respiratory distress after 10(9) CA, and pulmonary microvascular permeability was amplified. These changes evolved without increased candidemia or elevations in bioactive or antigenic serum TNF, which remained low even at death (42.3 +/- 14.8 U/ml vs. 12.6 +/- 2.9 U/ml for CY + saline, means +/- SE, P = NS). In contrast, significant TNF in lung tissue and bronchoalveolar lavage fluid (BALF) was evident within 6 h in CY + 10(9) CA rats. Electron microscopy confirmed hyphal proliferation into alveoli from yeast within mononuclear cells in lung capillaries. Subacute disseminated candidiasis after 10(6) CA was not associated with elevated serum, lung, or BALF TNF. We conclude that differential systemic and intrapulmonary TNF production occur in CA septic shock during preexisting neutropenia, with compartmentalized TNF production in the lower respiratory tract accompanying yeast-mycelial transformation. Thus TNF is not an obligate mediator of acute candidemic shock or subacute disseminated candidiasis during CY-induced immunosuppression but may initiate pulmonary injury accompanying high-grade candidemia.

Acute Disease↗
PubMed1984

Distance distortions in children's cognitive maps: an examination of the information storage model.

Second graders (mean age = 7-8), fourth graders (mean age = 9-8), and sixth graders (mean age = 11-11) walked two paths located in and around their school. Children in the Unsegmented condition estimated the distance and time taken to walk a path that was relatively undifferentiated in terms of the number of qualitatively different areas of the school through which it passed. Children in the Segmented condition made the same estimates for a path that went through different areas (segments) of the school (i.e., cafeteria, hall, vestibule, and outside the building). Children at all three grade levels estimated that the distance traversed in the Segmented condition was longer than the distance in the Unsegmented condition. This difference was not significant on the time measure. It was concluded that (1) paths with a large number of segments are perceived as being longer than paths of the same length with fewer segments, (2) distances along paths with few segments are underestimated, (3) distances along paths with many segments may be overestimated as a function of developmental level, and (4) only younger children may have used time to estimate distance.

Child↗
PubMed1984

Malpractice.

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Humans↗