Volume 15, Number 10—October 2009
Dispatch
Immunologic Response of Unvaccinated Workers Exposed to Anthrax, Belgium
, Marc Govaerts, Dimitrios Frangoulidis, David Fretin, Esther Kissling, Mieke Van Hessche, Bernard China, Martine Poncin, Yvo Pirenne, and Germaine Hanquet
Table
Number of workers showing immunoreactivity against Bacillus anthracis antigens, as assayed by 3 different methods*
| Status | Anti-PA ELISA† |
Western blot/dot blot‡ |
LT proliferation§ |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Year 1 | Year 2 | Year 1 | Year 2 | Ag = PA | Ag = LF | Ag = PA + LF | Ag = conA | |||
| Negative | 62 | 48 | – | – | 52 | 53 | 54 | 13 | ||
| Positive | 3 | 2 | 4 | 6 | 2¶ | 1¶# | 0 | 41 | ||
| Borderline | 1 | 4 | – | – | 0 | 0 | 0 | 0 | ||
*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.