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K M Cunnion

Publications and source records attributed to K M Cunnion.

8 recordsLinked to original sources
PubMed2004

Cleavage of complement C3b to iC3b on the surface of Staphylococcus aureus is mediated by serum complement factor I.

Complement-mediated opsonization of Staphylococcus aureus bearing the dominant capsule serotypes, serotypes 5 and 8, remains incompletely understood. We have previously shown that complement plays a vital role in the efficient phagocytosis of a serotype 5 S. aureus strain and that the opsonic fragments of the central complement protein C3, C3b and iC3b, were present on the bacterial surface after incubation in human serum. In the present studies, C3b and iC3b were found on several serotype 5 and 8 S. aureus strains after incubation in human serum. Using purified classical activation pathway complement proteins and the Western blot assay, we showed that when C3b was generated on the S. aureus surface no iC3b fragments were found, suggesting that other serum proteins may be required for cleaving C3b to iC3b. When C3b-coated S. aureus was incubated with serum factor I, a complement regulatory protein, iC3b was generated. Purified factor H, a serum protein cofactor for factor I, did not enhance factor I-mediated cleavage of C3b. These findings suggest that C3b cleavage to iC3b on S. aureus is mediated by serum factor I and does not require factor H.

Cell Membrane↗
PubMed2003

Availability of complement bound to Staphylococcus aureus to interact with membrane complement receptors influences efficiency of phagocytosis.

Complement-mediated opsonization of encapsulated Staphylococcus aureus (CP+) of the predominant capsule types, 5 and 8, remains poorly understood. Our previous work showed that complement is important for mouse survival of CP+ type 5 bacteremia and that the type 5 capsule inhibits the binding of opsonic C3 fragments to the organism. The importance of complement-mediated opsonization of CP+ was tested by neutrophil phagocytosis assays. Complement-mediated opsonization of CP+ increased phagocytosis by 57% compared to opsonization in complement-inhibited serum. Agar-grown CP+, enhancing capsule expression, was phagocytosed only one-tenth as well as the capsule-negative organisms (CP-), supporting the belief that staphylococcal polysaccharide capsules impair phagocytosis. Despite relatively poor phagocytosis of CP+ compared to CP-, complement activation increased the phagocytosis of CP+ by 103%. Thus, complement in normal human serum may have an important role in opsonizing CP+, even when capsule expression is strong. The ability of bound C3 fragments to interact with complement receptor 1 (CD35) on the membrane of human erythrocytes was tested in an immune adherence assay. S. aureus capsule was able to mask C3 fragments on the organism from binding to complement receptor 1. The inhibition of C3 binding to CP+ and the masking of deposited C3 fragments caused by the presence of capsule was associated with markedly decreased phagocytosis. The addition of anti-capsule antibodies to normal human serum was found to markedly improve the recognition of deposited C3 fragments by complement receptor 1 even when the absolute number of C3 molecules bound to S. aureus was not increased.

Antibodies, Bacterial↗
PubMed2003

Complement activation influences Staphylococcus aureus adherence to endothelial cells.

The ability of Staphylococcus aureus to adhere to endothelial cells (EC) is a critical step in the development of metastatic infection. The role of complement in S. aureus binding to EC remains uninvestigated. Log-phase S. aureus, expressing minimal capsule, was incubated with serum under various conditions, washed, and then incubated at 37 degrees C for 30 min with cultured human umbilical vein EC (ATCC CRL-1730). Adherence was scored visually after staining with acridine orange. Incubation in 10% heat-inactivated human serum increased adherence to endothelial cells by 488% compared to organisms incubated in buffer. Incubating S. aureus in complement-active normal human serum (NHS) decreased binding to EC by 58% compared to organisms incubated in heat-inactivated serum. The importance of active complement was confirmed by experiments using serum with added EDTA or cobra venom factor, a protein that depletes C3. The expression of capsule by S. aureus strongly interfered with adherence. It has been shown that an important protein for S. aureus adhesion to EC is fibronectin. S. aureus adherence to purified fibronectin increased by 511% after incubation in heat-inactivated serum, compared to that of organisms incubated in buffer. This decreased by 56% in complement-active serum, suggesting that inhibition of S. aureus adherence to EC is due, in part, to complement-mediated diminished binding to fibronectin. Interestingly, when EC were exposed to S. aureus-activated serum and then washed, binding by S. aureus was 234% higher than that of EC exposed to NHS. Thus, complement-activated EC have increased S. aureus binding, while complement on the bacterial surface markedly reduces adherence.

Bacterial Adhesion↗
PubMed2001

Capsule production and growth phase influence binding of complement to Staphylococcus aureus.

Complement-mediated opsonization of bacteria by C3 binding is an important component of the host innate immune system. Little information is available concerning the interaction between complement proteins and capsule type 5 and 8 Staphylococcus aureus strains, even though these isolates are responsible for approximately 70% of human staphylococcal infections. To investigate the importance of an intact complement pathway in an experimental staphylococcal infection, control and C3-depleted mice were challenged intravenously with 10(7) CFU of a serotype 5 S. aureus isolate. Whereas only 8% of the control mice succumbed to the infection, 64% of the complemented-depleted animals died. In vitro parameters of C3 binding to two heavily encapsulated (CP++) strains, three encapsulated (CP+) strains, and an isogenic capsule-negative (CP-) mutant were examined. The alternative pathway contributed 90% of C3 binding in 20% serum at 30 min, whereas it accounted for only 13% of C3 binding in 2% serum. Stationary-phase organisms bound only 10% as much C3 as mid-log-phase organisms; this was only in part due to capsule. When the S. aureus strains were cultivated on solid medium, the CP++ isolates bound 50% less C3 than CP+ strains; a CP+ strain bound 42% less C3 than the CP- mutant. Both C3b and iC3b fragments of C3 bound to S. aureus cells, and about one-third of the bound C3 was shed from the staphylococcal surface as iC3b, regardless of the CP phenotype of the strain. Thus, the phase of growth and presence of capsule are critical to opsonization.

Agammaglobulinemia↗
PubMed1999

Tumor necrosis factor receptors encoded by poxviruses.

Poxviruses encode several cytokine response modifying (Crm) proteins. The Crm proteins possess sequence homology to several human proteins important in immunity. This homology and the conservation of Crm proteins among poxvirus strains suggest an immunomodulatory function that provides a survival advantage to the virus. Cowpox virus encodes several tumor necrosis factor (TNF) receptor family homologues: CrmB, CrmC, and CrmD. CrmB and CrmD encode a similar approximately 155 amino acid COOH-terminus region distal to their TNF ligand-binding portions. These C-terminus regions contain no significant homology with sequences in public databases. It is not known whether the C-terminus regions have a complementary function to the TNF ligand-binding domains, or an unrelated function. Myxoma virus, a rabbit poxvirus, encodes a protein termed T2 which is homologous to CrmB and CrmD. Deletion of the T2 gene results in decreased pathogenicity of myxoma in rabbits. T2 has also been shown to interfere with TNF-induced apoptosis in vitro. Understanding the role viral TNF receptor homologues play in altering host immune responses may suggest ways to develop specific anti-inflammatory therapeutics.

Animals↗
PubMed1996

Risk factors for nosocomial pneumonia: comparing adult critical-care populations.

The purpose of the study was to examine risk factors for nosocomial pneumonia in the surgical and medical/respiratory intensive care unit (ICU) populations. In a public teaching hospital, all cases of nosocomial pneumonia in the surgical and medical/respiratory ICUs (n = 20, respectively) were identified by prospective surveillance during a 5-yr period from 1987-1991. Each group of ICU cases was compared with 40 ICU control patients who did not acquire pneumonia, and analyzed for 25 potential risk factors. Surgical ICU patients were found to have consistently higher rates of nosocomial pneumonia than medical ICU patients (RR = 2.2). The strongest predictor for nosocomial pneumonia in both the surgical and medical/respiratory ICU groups was found to be prolonged mechanical ventilation (> 1 d) resulting in a 12-fold increase in risk over nonventilated patients. APACHE III score was found to be predictive of nosocomial pneumonia in the surgical ICU population, but not in the medical/respiratory ICU population. We conclude that certain groups deserve special attention for infection control intervention. Surgical ICU patients with high APACHE scores and receiving prolonged mechanical ventilation may be at the greatest risk of acquiring nosocomial pneumonia of all hospitalized patients.

APACHE↗