Learning from the 2001 anthrax attacks: immunological characteristics.

Potential conflicts of interest: none reported. The views expressed in this commentary are those of the author and do not necessarily reflect the official policy or position of the Connecticut Department of Public Health. The article by Doolan et al. in this issue of the Journal of Infectious Diseases [1] describes the immune responses to anthrax among persons exposed and possibly exposed when a letter containing spores that had been sent to Senator Daschle was opened in the Hart Senate Office Building (HSOB) in October 2001. The authors took advantage of this unfortunate but unique opportunity to conduct an observational study to determine whether high levels of inhalational exposure to anthrax spores resulted in clinical disease, as well as in humoral immune or cell-mediated immune (CMI) responses. This is one of the few studies of the immune response to high-level, naturally occurring anthrax exposure in humans, and it may be the first to describe CMI responses to this pathogen. The immune responses of persons with various levels of exposure, including an unexposed group and an unexposed but recently vaccinated group, are described, with data collected at 3 points in time: ∼6, 8, and 12 weeks after exposure. The degree of exposure was determined by proximity in the HSOB and Capitol complex to the letter at the time when it was opened. The proximity measure of exposure correlated directly with the percentage in each group who had positive nasopharyngeal cultures within 24 h of the incident. In addition, the article describes the immune response to vaccination against anthrax among the subset of these groups who were vaccinated as part of the public health response. The key findings are that, although all highly exposed persons had immediately received antibiotics and there was no evidence that exposure resulted in clinical illness, sizeable percentages of persons highly exposed but not vaccinated had evidence of either humoral immune (40% to protective an-tigen [PA] and 14% to lethal factor [LF]) or CMI (80% to PA and ∼60% to LF) responses. In addition, immune responses occurred mainly in persons with higher levels of exposure, and, for all measures of immunity, there was a notable dose-response gradient. Vaccination of highly exposed persons also provoked detectable anti-LF antibodies in up to 40% of vac-cinees. No one in the recently vaccinated, unexposed control group had detectable anti-LF antibodies; the anthrax vaccine used (anthrax vaccine adsorbed [AVA]) is geared toward the …