Racial Differences in Neutrophil Response.

Abstract

Bacterial lipopolysaccharide (LPS), or endotoxin, is a mediator of inflammation. Repeated translocation of endotoxin from oral and intestinal bacteria into the bloodstream has been associated with low-grade systemic inflammation which in-turn increases the risk for systemic disease. A recent IUSD study linked experimental gingivitis to low-grade endotoxemia in both African-Americans and Caucasians. Interestingly, the study also reported differences in neutrophil numbers and oxidative burst activity between the two races. The aim of this preliminary study was to assess the in vitro neutrophil response to low dose LPS priming and subsequent activation with formyl-methionyl-leucyl-phenylalanine (fMLP) by Caucasian (C, n=6) and African American (AA, n=6) males 18 – 40 years of age. Following 6% polysucrose sedimentation of whole blood to reduce red blood cell contamination, fresh neutrophils were isolated by centrifugation over Histopaque® separation media. Neutrophils were resuspended in RPMI medium supplemented with 5% autologous serum, primed with 1 ng/ml LPS for 30 or 60 min and then activated with fMLP. Subsequently, cell-free culture media were collected, aliquoted and stored frozen until tested by ELISA for levels of myeloperoxidase (MPO), bactericidal permeability increasing protein (BPI) and acyloxyacyl hydrolase (AOAH) as markers of neutrophil activation. Activated neutrophils from C subjects released significantly higher levels of BPI compared to AA subjects (p=0.0077 & 0.0197, 30 and 60 minute prime, respectively). Similarly, the mean MPO levels in culture supernatants were higher for C males although the differences were not significant. AOAH was undetectable in the cell culture supernatants. In conclusion, neutrophils from C males displayed a stronger response (BPI and MPO) to LPS than neutrophils from AA male subjects suggesting a biological basis for the reported racial disparity in neutrophil response. (Supported by the IUPUI Office of the Vice Chancellor for Research)