Salmonella typhi flagella are potent inducers of proinflammatory cytokine secretion by human monocytes - PubMed (original) (raw)

Salmonella typhi flagella are potent inducers of proinflammatory cytokine secretion by human monocytes

T L Wyant et al. Infect Immun. 1999 Jul.

Abstract

The cytokine production patterns of human peripheral blood mononuclear cells (PBMC) in response to Salmonella typhi flagella (STF) were examined in culture supernatants of PBMC stimulated with STF. Consistent with previous findings in volunteers vaccinated with aroC aroD deletion mutants of S. typhi, PBMC from volunteers immunized with the licensed live Ty21a S. typhi vaccine secreted gamma interferon following exposure to STF. Stimulation with STF induced rapid de novo synthesis of tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta), followed by IL-6 and IL-10. Trypsin treatment of STF abrogated their effects, while polymyxin B had no effect. Intracellular cytokine measurements of STF-stimulated PBMC revealed the existence of monocyte subpopulations that produce only TNF-alpha, IL-1beta or both cytokines. Moreover, STF markedly decreased the percentage of CD14(+) cells. These data demonstrate that STF are powerful monocyte activators which may have important implications for vaccine development and for understanding the pathogenesis of S. typhi infection.

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Figures

FIG. 1

Induction of cytokine production by human PBMC after exposure to STF. Cytokine production was measured in culture supernatants 4 days after incubation in the absence (media) or presence of STF (4 μg/ml), TT (2 μg/ml), the malarial repeat antigen NANP (4 μg/ml), or BSA (4 μg/ml). These results are representative of those observed in 10 individual volunteers, all of whom were immunized orally with the attenuated Ty21a S. typhi strain.

FIG. 2

Time course of secretion of cytokines after exposure to STF. Human PBMC were cultured in the absence (media) or presence of STF (4 μg/ml) or TT (2 μg/ml). Culture supernatants were collected at various time points, and the concentrations of TNF-α, IL-1β, IL-10, and IFN-γ were determined. These results are representative of those observed with cells obtained from three different individuals immunized orally with the attenuated Ty21a S. typhi strain.

FIG. 3

STF induction of increased intracellular levels of IL-1β and/or TNF-α in human monocytes. The percentages of cells containing intracellular IL-1β and TNF-α were determined in PBMC from four individuals 5 h after addition of STF (4 μg/ml) or TT (2 μg/ml). Data are mean percentages of positive cells ± standard deviation (SD) from the four volunteers. (A) Representative example of the high forward scatter/high side scatter region which was used to define the monocyte population. In the experiment shown, 30.5% of the total cells were contained in the monocyte region after stimulation with TT, while 24.1% of the cells were contained within the monocyte region after STF stimulation. In this experiment, the percentage of cells contained within the monocyte region in unstimulated cultures (media) was 35.0%. (B) Percentage of CD14+ cells within the monocyte region in unstimulated cultures (media) or after STF or TT stimulation. (C) Mean percentage of cells containing IL-1β and/or TNF-α ± SD in cells within the monocyte region in the four volunteers. Results shown correspond to four different volunteers, two unvaccinated and two immunized with the attenuated Ty21a S. typhi strain. Asterisks denote P of <0.01 by paired t test, compared with untreated cultures or cultures incubated with TT; two-tailed P values are shown.

FIG. 4

Flow cytometric analysis showing distribution of human PBMC containing IL-1β and/or TNF-α induced by STF or TT. PBMC from a volunteer immunized with the attenuated Ty21a S. typhi strain were incubated for 5 h with methylamine plus monensin in the absence or presence of TT (2 μg/ml) (left) or STF (4 μg/ml) (right). Cells were then stained intracellularly for IL-1β and TNF-α. Cytograms showing the distribution of cells within the monocyte region containing either IL-1β (lower right quadrants), TNF-α (upper left quadrants), or both cytokines (upper right quadrants) are presented. The percentage of positive cells in each of the quadrants is shown. These results are representative of those observed with cells obtained from three different individuals, one unvaccinated and two immunized with the attenuated Ty21a S. typhi strain.

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Salmonella typhi flagella are potent inducers of proinflammatory cytokine secretion by human monocytes - PubMed (original) (raw)