Monoclonal Antibodies Against the Staphylococcus aureus Bicomponent Leukotoxin AB Isolated Following Invasive Human Infection Reveal Diverse Binding and Modes of Action.

The 2-component leukotoxin LukAB is critical for Staphylococcus aureus targeting and killing of human neutrophils ex vivo and is produced in the setting of human infection. We report 3 LukAB-specific human monoclonal antibodies (mAbs) with distinct mechanisms of toxin neutralization and in vivo efficacy. Three hybridomas secreting mAbs with anti-LukAB activity (designated SA-13, -15, and -17) were generated from B cells obtained from a 12-year-old boy with S. aureus osteomyelitis. Each of the 3 mAbs neutralized LukAB-mediated neutrophil toxicity, exhibited differing levels of potency, recognized different antigenic sites on the toxin, and displayed at least 2 distinct mechanisms for cytotoxic inhibition. SA-15 bound exclusively to the dimeric form of the toxin, suggesting that human B cells recognize epitopes on the dimerized form of LukAB during natural infection. Both SA-13 and SA-17 bound the LukA monomer and the LukAB dimer. Although all 3 mAbs potently neutralized cytotoxicity, only SA-15 and SA-17 significantly inhibited toxin association with the cell surface. Treatment with a 1:1 mixture of mAbs SA-15 and SA-17 resulted in significantly lower bacterial colony counts in heart, liver, and kidneys in a murine model of S. aureus sepsis. These data describe the isolation of diverse and efficacious antitoxin mAbs.

Commercial Intravenous Immunoglobulin Preparations Contain Functional Neutralizing Antibodies against the Staphylococcus aureus Leukocidin LukAB (LukGH).

The pathogenesis of Staphylococcus aureus is mediated by an array of important virulence factors, including the two-component leukocidin family of toxins. LukAB (also known as LukGH), the most recently discovered leukocidin, is potently lethal to phagocytes, produced during invasive human disease, and present in all known clinical isolates of S. aureus Intravenous immunoglobulin (IVIg) is often used clinically in severe S. aureus infections. The primary aim of this study was to assess the binding and neutralization potential of IVIg against LukAB. A secondary aim was to examine the lot-to-lot variability of IVIg in the binding and neutralization of LukAB. We studied 24 distinct lots of IVIg and compared them to serum from children with invasive S. aureus infection (in the acute and convalescent phases) and from healthy, uninfected controls. We found that all lots of IVIg contained functional antibodies targeting LukAB. After adjusting for total antibody content per sample, we found that the amount of anti-LukAB antibody in IVIg was similar to that seen with healthy controls and less than that seen with patients with invasive S. aureus infection. IVIg samples had lower neutralization capacity than samples from healthy controls and children with invasive infection. IVIg had remarkably little lot-to-lot variation in LukAB binding but had significantly more variation in toxin neutralization. These results represent the first report of functional antibodies against the important S. aureus leukocidin LukAB in IVIg. Given the frequent clinical use of IVIg for severe S. aureus infections, improving our understanding of functional antibody properties exhibited by this therapeutic is essential.

Rationale and design for eHealth Familias Unidas Primary Care: A drug use, sexual risk behavior, and STI preventive intervention for hispanic youth in pediatric primary care clinics.

Family-based behavioral interventions are efficacious and effective in preventing drug use and sexual risk behaviors; unfortunately, they have not been evaluated and disseminated in pediatric primary care practice, where they can have a significant impact. There is an increased focus on integrating parenting interventions into primary care to reduce health disparities among ethnic minorities such as Hispanics. Although Hispanic youth demonstrate higher levels of drug use and sexual risk behaviors than their non-Hispanic counterparts, few parenting interventions are available for Hispanic youth, and none have been delivered specifically to Hispanic adolescents in primary care. Therefore, this manuscript describes the rationale and design of an Internet-based, family-centered, Hispanic-specific, evidence-based prevention intervention, eHealth Familias Unidas Primary Care. Hispanic adolescents (n = 456) and their care givers will be recruited from pediatric primary care clinics in South Florida and randomized to: eHealth Familias Unidas Primary Care or prevention as usual. The intervention will be delivered by trained interns, clinic volunteers, social workers, mental health counselors, students, and nurses. Outcomes will be measured at baseline and 6, 12, 24, and 36 months post-baseline. This study will determine whether the intervention, compared to prevention as usual, is effective in reducing drug use, unprotected sex, and STI incidence in Hispanic youth through the improvement of family functioning. Additionally, we will determine the cost effectiveness of delivering eHealth Familias Unidas within primary care settings. The effectiveness of eHealth Familias Unidas Primary Care will further inform the need to integrate effective behavioral health interventions into primary care settings.