Biomedical subjects

Pamela S Hair

Publications and source records attributed to Pamela S Hair.

3 recordsLinked to original sources

PubMed2005

Serum complement factor I decreases Staphylococcus aureus phagocytosis.

Complement-mediated opsonization of Staphylococcus aureus is a critical host defense in animal models. Specifically, C3b and CD35 play important roles in effective opsonophagocytosis of S. aureus. We have shown that complement control protein factor I mediates cleavage of the complement opsonin C3b bound to the S. aureus surface. In this study, we examined the physiologic relevance of this observation by determining whether factor I-mediated cleavage of S. aureus-bound C3b decreased phagocytosis of S. aureus by neutrophils. Compared with controls, anti-factor I antibody inhibited C3b-cleavage on the S. aureus surface by >83% (as measured by iC3b generation) and increased phagocytosis of S. aureus by >100%. Treatment of C3b-coated S. aureus with factor I increased generation of iC3b (75%), decreased the total amount of C3-fragments bound to the S. aureus surface (58%), and decreased the number of bacteria phagocytosed (40%). Testing specifically for C3-fragments shed from the S. aureus surface, we found that factor I increased shedding (43%). Notably, these factor I-mediated effects were of the same magnitude regardless of whether factor H, a known cofactor for factor I, was present. These findings indicate that S. aureus benefits from, and possibly manipulates, the normally host-protective activity of factor I cleavage of C3b, which results in bacterial escape from complement-mediated opsonophagocytosis. Because escaping opsonophagocytosis-mediated destruction is a necessary mechanism for bacterial survival resulting in human disease, preventing cleavage of C3b on the S. aureus surface, and thereby enhancing opsonophagocytosis, is a promising potential target for therapeutic intervention.

Antibodies, Blocking↗

PubMed2003

The effects of intense submicrosecond electrical pulses on cells.

A simple electrical model for living cells predicts an increasing probability for electric field interactions with intracellular substructures of both prokaryotic and eukaryotic cells when the electric pulse duration is reduced into the sub-microsecond range. The validity of this hypothesis was verified experimentally by applying electrical pulses (durations 100 micros-60 ns, electric field intensities 3-150 kV/cm) to Jurkat cells suspended in physiologic buffer containing propidium iodide. Effects on Jurkat cells were assessed by means of temporally resolved fluorescence and light microscopy. For the longest applied pulses, immediate uptake of propidium iodide occurred consistent with electroporation as the cause of increased surface membrane permeability. For nanosecond pulses, more delayed propidium iodide uptake occurred with significantly later uptake of propidium iodide occurring after 60 ns pulses compared to 300 ns pulses. Cellular swelling occurred rapidly following 300 ns pulses, but was minimal following 60 ns pulses. These data indicate that submicrosecond pulses achieve temporally distinct effects on living cells compared to microsecond pulses. The longer pulses result in rapid permeability changes in the surface membrane that are relatively homogeneous across the cell population, consistent with electroporation, while shorter pulses cause surface membrane permeability changes that are temporally delayed and heterogeneous in their magnitude.

Cell Membrane↗

PubMed2003

Sub-microsecond, intense pulsed electric field applications to cells show specificity of effects.

Application of sub-microsecond duration (60-300 ns), intense (15-60 kV/cm) pulsed electric fields (sm/i-PEF) to six types of human cells was examined for its effects on individual cell surface membrane permeability and membrane potential. With short (60 ns) pulses, increasing percentages of Jurkat cells showed propidium iodide (PI) uptake at progressively shorter post-pulse times as the pulse train increased from 1 to 10 sequential pulses, while human blood polymorphonuclear leukocytes (PMN) were unresponsive to these short pulses regardless of train size. With 300 ns pulses, a similar pattern (increasing percentages of cells taking up PI, and progressively shorter times of onset after pulse applications as pulse train size increased) was seen with both Jurkat cells and PMN, but the patterns for both effects were different. Jurkat cell size did not appear to influence the responsiveness of this cell type. Comparisons of sm/i-PEF-induced PI uptake by human monocyte-derived macrophages vs. aged human mononuclear cells, human trunk skin (HTS) cells vs. fresh human mononuclear cells and human macrophages vs. HTS cells showed similar overall effects, but with differences between the patterns for each cell type compared (except the macrophages vs. HTS cells comparison). Application of sm/i-PEFs also caused different patterns of membrane potential loss in Jurkat cells vs. PMN. Jurkat cells developed significant decreases in t heir membrane potential only following the highest intensity pulse applications examined, i.e., 300 ns, 60 kV/cm x5, while PMN showed this effect over the entire range of pulse intensities (300 ns, 15-60 kV/cm, x5) applied. These data indicate that sm/i-PEF applications can have "specificity" (i.e., achieve different levels of effect in different cell types), that cell size does not appear to be the major factor determining sm/i-PEF effects in either Jurkat cells or PMN, that heterogeneous sm/i-PEF effects on cells tend to become homogeneous with increasing pulse train size, and that specificity of sm/i-PEF applications effects can occur at either end of the sm/i-PEF intensity spectrum examined.

Age Factors↗