Search

Panton Valentine leukocidin (PVL) may be responsible for pulmonary necrosis in necrotizing Staphylococcus aureus pneumonia, a highly lethal infection. Commercial intravenous immunoglobulin (IVIg) preparations containing antibodies against PVL might have therapeutic value in this setting, as an adjunct to antimicrobial chemotherapy. To test this possibility, we determined anti-PVL antibody titers in commercial IVIg and the capacity of IVIg to prevent the cytopathic effects of PVL in vitro. Specific enzyme-linked immunosorbent assays based on purified recombinant PVL (rPVL) showed that IVIg contained specific anti-PVL antibodies. The cytotoxicity of rPVL and of crude culture supernatants of PVL-producing S. aureus strains were investigated by measuring ethidium-bromide incorporation by polymorphonuclear neutrophils (PMNs) in flow cytometric assays, as well as PMN ultrastructural changes by transmission electron microscopy. IVIg was found to neutralize pore formation and the cytopathic effect of both rPVL and S. aureus culture supernatants.

The binding of the S component (LukS-PV) from the bicomponent staphylococcal Panton-Valentine leucocidin to human polymorphonuclear neutrophils (PMNs) and monocytes was determined using flow cytometry and a single-cysteine substitution mutant of LukS-PV. The mutant was engineered by replacing a glycine at position 10 with a cysteine and was labeled with a fluorescein moiety. The biological activity of the mutant was identical to that of the native protein. It has been shown that LukS-PV has a high affinity for PMNs (Kd = 0.07 +/- 0.02 nM, n = 5) and monocytes (Kd = 0.020 +/- 0.003 nM, n = 3) with maximal binding capacities of 197,000 and 80,000 LukS-PV molecules per cell, respectively. The nonspecifically bound molecules of LukS-PV do not form pores in the presence of the F component (LukF-PV) of leucocidin. LukS-PV and HlgC share the same receptor on PMNs, but the S components of other staphylococcal leukotoxins, HlgA, LukE, and LukM, do not compete with LukS-PV for its receptor. Extracellular Ca2+ at physiological concentrations (1 to 2 nM) has only a slight influence on the LukS-PV binding, in contrast to its complete inhibition by Zn2+. The down-regulation by phorbol 12-myristate 13-acetate (PMA) of the binding of LukS-PV was blocked by staurosporine, suggesting that the regulatory effect of PMA depends on protein kinase C activation. The labeled mutant form of LukS-PV has proved very useful for detailed binding studies of circulating white cells by flow cytometry. LukS-PV possesses a high specific affinity for a unique receptor on PMNs and monocytes.

Panton-Valentine leukocidin (PVL) is a cytotoxin that causes leukocyte destruction and tissue necrosis. It is produced by fewer than 5% of Staphylococcus aureus strains. A collection of 172 S. aureus strains were screened for PVL genes by polymerase chain reaction amplification. PVL genes were detected in 93% of strains associated with furunculosis and in 85% of those associated with severe necrotic hemorrhagic pneumonia (all community-acquired). They were detected in 55% of cellulitis strains, 50% of cutaneous abscess strains, 23% of osteomyelitis strains, and 13% of finger-pulp-infection strains. PVL genes were not detected in strains responsible for other infections, such as infective endocarditis, mediastinitis, hospital-acquired pneumonia, urinary tract infection, and enterocolitis, or in those associated with toxic-shock syndrome. It thus appears that PVL is mainly associated with necrotic lesions involving the skin or mucosa.