839. Children with Invasive Staphylococcal Disease Exhibit a Potent Neutralizing Antibody Response to the Newly Described Cytotoxin, LukAB/LukGH
Session: Oral Abstract Session: Innate and Adaptive Immunity to Infections
Saturday, October 22, 2011: 9:00 AM
Room: 156ABC

Background: Staphylococcus aureus (SA) has become the most common invasive bacterial pathogen in the US. Despite this organism's importance, the humoral response to staphylococcal infection in humans remains inadequately defined. SA produces many extracellular virulence determinants, such as alpha-toxin, V8 protease, and Panton-Valentine Leukocidin (PVL). LukAB/LukGH is a newly described, potent leukotoxin produced abundantly by SA and is critical in animal models of pathogenesis.

Methods: We are prospectively enrolling children 6 months – 18 years with culture-proven SA infection, stratified by disease type (invasive vs. non-invasive). Serum samples are obtained acutely (≤48 hours after culture identification) and during convalescence (~4 weeks after disease onset). Serum IgG concentrations are determined by indirect ELISA for alpha-toxin, V8 protease, PVL, and LukAB/LukGH. Toxin neutralization is assessed by measuring viability of PMN-HL60 cells one hour after intoxication with LukAB/LukGH in the presence or absence of patient sera.

Results: Of the 22 children enrolled thus far with invasive SA disease, 20 (91%) exhibited an acute serum IgG response to the LukA/H subunit of LukAB/LukGH detectable at a dilution of at least 1:40, with 15 of these (75%) demonstrating a high-titer response of ≥1:320. While 17/22 patients had detectable antibodies (≥1:40) to alpha-toxin and the LukB/G subunit of LukAB/LukGH (77%), 15/22 to V8 protease (68%), and 13/22 to PVL (59%), LukA/H generated greater signal intensity by ELISA at the highest dilutions.  Three additional patients developed a four-fold increase in convalescent titers against the LukB/G subunit of LukAB/GH (14%), and one patient had a four-fold rise in anti-alpha-toxin IgG (5%). Acute and convalescent sera with detectable anti-LukAB/LukGH antibodies potently neutralized cytotoxicity in vitro (Figure 1).

Conclusion: This novel description of a high-titer neutralizing antibody response to LukAB/LukGH confirms its prominence in the SA secretome and adds to the recognition of this cytotoxin as an important component of staphylococcal disease.

Figure 1:  Neutralization of LukAB/LukGH. WT = toxin alone; ΔlukAB = toxin deleted; IgG = WT with rabbit IgG; a-LukA = Rabbit anti-LukA.


Subject Category: E. Innate and adaptive immunity to infections, including vaccine immunology

Isaac Thomsen, MD, Pediatric Infectious Diseases, Monroe Carell, Jr. Children's Hospital at Vanderbilt, Nashville, TN, Elizabeth Saye, B.S., Vanderbilt University Medical Center, Nashville, TN, Victor Torres, Ph.D., Microbiology, New York University School of Medicine, New York, NY and C. Buddy Creech, MD, MPH, Pediatric Infectious Diseases and Vanderbilt Vaccine Research Program, Vanderbilt University School of Medicine, Nashville, TN

Disclosures:

I. Thomsen, None

E. Saye, None

V. Torres, None

C. B. Creech, None

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