Volume 15, Number 10—October 2009
Immunologic Response of Unvaccinated Workers Exposed to Anthrax, Belgium
||Western blot/dot blot‡
|Year 1||Year 2||Year 1||Year 2||Ag = PA||Ag = LF||Ag = PA + LF||Ag = conA|
*PA, protective antigen; LT, lymphocyte; Ag, antigen; LF, lethal factor; conA, concanavalin A.
†Performed on serum samples according to the manufacturer’s instructions and thresholds (Serion, Würzburg, Germany). Note: 1 worker who tested positive at year 1 was not enrolled at year 2, and 3 workers tested negative at year 1 seroconverted to borderline at year 2.
‡Conducted only on serum samples found positive or borderline by anti-PA ELISA together with negative controls (n = 25). Dot blots were spotted with 1,000, 100, 10, and 1 ng of each purified PA and LF Ag purchased from Quadratech Ltd. (Epson, UK). Western blot antigens consisted in supernatant proteins derived from the culture of a reference B. anthracis strain.
§Assayed on blood samples from year 2 as described earlier (9) by using a proliferative index threshold set to 3× the index of a negative control stimulant (phosphate buffer). Stimulating Ag was used at a final concentration of 4 mg/mL (PA, LF, conA). ConA was used as positive control stimulant and was purchased from Sigma (St. Louis, MO, USA). Lymphocyte cultures found activatable by PA were confirmed by quantifying IFN-γ release by ELISA, according to the manufacturer’s instructions (Pierce, Rockford, IL, USA).
¶Serum samples from these workers tested positive by both Western blot and dot blot analysis.
#This culture was also stimulated by PA.