Acute systemic immune activation following conjunctival exposure to staphylococcal enterotoxin B

Abstract

Conjunctival exposure to the Staphylococcus aureus superantigen staphylococcal enterotoxin B (SEB) may occur accidentally, as a result of bioterrorism, or during colonization or infection of the external eye. Using human leukocyte antigen class II transgenic mice, we show for the first time that conjunctival exposure to SEB can cause robust systemic immune activation.

FIG. 1.

Systemic T-cell activation after conjunctival exposure to SEB. Age-matched HLA-DQ8.IL-10^−/− mice were anesthetized, and 5 μl (25 μg) of SEB was applied onto each eye. The expression of activation markers CD62L (A) and CD69 (B) on SEB-reactive TCR Vβ8⁺ CD4⁺ and CD8⁺ T cells in the cervical lymph nodes at the indicated time points was determined by flow cytometry. Representative histograms from one of four similar experiments are shown.

FIG. 2.

Peripheral T-cell expansion after conjunctival exposure to SEB. Age-matched HLA-DQ8.IL-10^−/− mice were anesthetized, and 5 μl (25 μg) of SEB was applied onto each eye. Mice were sacrificed at the indicated time points, and the distribution of CD4⁺ and CD8⁺ T cells expressing TCR Vβ6 (SEB-nonreactive) or Vβ8 (SEB-reactive) in the cervical lymph nodes (A) and spleens (B) was analyzed by flow cytometry. Bars represent mean + the standard error from four to five mice/group.

FIG. 3.

Thymocyte apoptosis after conjunctival exposure to SEB. Age-matched HLA-DQ8.IL-10^−/− mice were anesthetized, and 5 μl (25 μg) of SEB was applied onto each eye. Mice were sacrificed at the indicated time points, and the distributions of thymocyte subsets were analyzed by flow cytometry. Representative dot plots from one of four similar experiments are shown.

FIG. 4.

Peripheral T-cell expansion after conjunctival exposure to SEB. Age-matched HLA-DR3 transgenic mice were anesthetized, and 5 μl (25 μg) of SEB was applied onto each eye. Mice were treated with BrdU in drinking water daily and sacrificed at 72 h. BrdU incorporated in CD4⁺ and CD8⁺ T cells expressing TCR Vβ6 (SEB-nonreactive) or Vβ8 (SEB-reactive) in cervical lymph nodes in gated population (indicated by the circles) was analyzed by flow cytometry. Representative plots are shown. In histograms, shaded and clear areas represent BrdU incorporated in Vβ6- and Vβ8-gated cells, respectively.