The Bacillus anthracis exosporium
protein BclA contains an O-linked antigenic tetrasaccharide whose terminal
sugar is known as
anthrose (J. M. Daubenspeck et al., J. Biol. Chem. 279:30945-30953, 2004). We hypothesized that serologic responses to
anthrose may have diagnostic value in confirming exposure to aerosolized B. anthracis. We evaluated the serologic responses to a synthetic
anthrose-containing
trisaccharide (ATS) in a group of five rhesus macaques that survived
inhalation anthrax following exposure to B. anthracis Ames spores. Two of five animals (RM2 and RM3) were treated with
ciprofloxacin starting at 48 hours postexposure and two (RM4 and RM5) at 72 h postexposure; one animal (RM1) was untreated.
Infection was confirmed by blood culture and detection of
anthrax toxin lethal factor (LF) in plasma. Anti-ATS
IgG responses were determined at 14, 21, 28, and 35 days postexposure, with preexposure serum as a control. All animals, irrespective of
ciprofloxacin treatment, mounted a specific, measurable anti-ATS
IgG response. The earliest detectable responses were on days 14 (RM1, RM2, and RM5), 21 (RM4), and 28 (RM3). Specificity of the anti-ATS responses was demonstrated by competitive-inhibition
enzyme immunoassay (CIEIA), in which a 2-fold (wt/wt) excess of
carbohydrate in a
bovine serum albumin (BSA) conjugate of the
oligosaccharide (ATS-BSA) effected >94% inhibition, whereas a structural analog lacking the 3-hydroxy-3-methyl-butyryl moiety at the C-4" of the anthrosyl residue had no inhibition activity. These data suggest that anti-ATS antibody responses may be used to identify
aerosol exposure to B. anthracis spores. The anti-ATS antibody responses were detectable during administration of
ciprofloxacin.