Understanding immune responses to native
antigens in response to natural
infections can lead to improved approaches to vaccination. This study sought to characterize the humoral immune response to
anthrax toxin components,
capsule and spore
antigens in individuals (n = 46) from the Kayseri and Malatya regions of Turkey who had recovered from mild or severe forms of
cutaneous anthrax infection, compared to regional healthy controls (n = 20).
IgG antibodies to each toxin component, the poly-γ-D-
glutamic acid capsule, the Bacillus
collagen-like
protein of anthracis (BclA) spore
antigen, and the spore
carbohydrate anthrose, were detected in the cases, with
anthrax toxin neutralization and responses to Protective
Antigen (PA) and Lethal Factor (LF) being higher following severe forms of the disease. Significant correlative relationships among responses to PA, LF,
Edema Factor (EF) and
capsule were observed among the cases. Though some regional control sera exhibited binding to a subset of the tested
antigens, these samples did not neutralize
anthrax toxins and lacked correlative relationships among
antigen binding specificities observed in the cases. Comparison of serum binding to overlapping decapeptides covering the entire length of PA, LF and EF
proteins in 26 cases compared to 8 regional controls revealed that
anthrax toxin-
neutralizing antibody responses elicited following natural
cutaneous anthrax infection are directed to conformational
epitopes. These studies support the concept of vaccination approaches that preserve conformational
epitopes.