RationaleAlterations in the composition of the gastrointestinal microbiota alter the immune system in the intestinal tract and at other mucosal sites. We examined whether antibiotic-induced alteration of the gastrointestinal microbiota affected the respiratory mucosal immune response to Sendai virus (SeV).MethodsTo alter the intestinal microbiota, mice were given water with or without the non-absorbable antibiotic streptomycin for 2 weeks. They were then intranasally inoculated with a non-lethal dose of SeV (2 x105 pfu). To deplete regulatory T cells (Treg), Foxp3-GFP-DTR mice were given diphtheria toxin intraperitoneally. Flow cytometry was used to quantify T cell subsets.ResultsAddition of streptomycin to the water led to a significantly increased mortality from SeV infection (81% versus 0%, n=23-26; p<0.0001). Surprisingly, the Treg number was decreased in the lung by 47% in mice given the antibiotic (streptomycin, 1.05+/-0.13 x105; n=4; versus no streptomycin, 2.0+/-0.18 x105; n=3; p=0.01). Similarly, Treg cells in the distal small intestine were decreased by 92% with streptomycin (1.57+/-1.28 x105; n=3; versus no streptomycin, 1.97+/-0.44 x106; n=3; p=0.03). To determine if reduced Tregs lead to increased mortality, Tregs were depleted in Foxp3-GFP-DTR mice, and we observed 100% mortality to SeV even in absence of streptomycin (n=4; p=0.01 versus PBS treatment).ConclusionsAdministration of streptomycin markedly increased mortality to SeV and was associated with decreased Treg cells in the gastrointestinal and respiratory tracts. Even in the absence of an antibiotic, depleting Tregs led to high mortality to SeV. Tregs may link gastrointestinal and respiratory mucosal immune systems, especially in response to respiratory viral infections. RationaleAlterations in the composition of the gastrointestinal microbiota alter the immune system in the intestinal tract and at other mucosal sites. We examined whether antibiotic-induced alteration of the gastrointestinal microbiota affected the respiratory mucosal immune response to Sendai virus (SeV). Alterations in the composition of the gastrointestinal microbiota alter the immune system in the intestinal tract and at other mucosal sites. We examined whether antibiotic-induced alteration of the gastrointestinal microbiota affected the respiratory mucosal immune response to Sendai virus (SeV). MethodsTo alter the intestinal microbiota, mice were given water with or without the non-absorbable antibiotic streptomycin for 2 weeks. They were then intranasally inoculated with a non-lethal dose of SeV (2 x105 pfu). To deplete regulatory T cells (Treg), Foxp3-GFP-DTR mice were given diphtheria toxin intraperitoneally. Flow cytometry was used to quantify T cell subsets. To alter the intestinal microbiota, mice were given water with or without the non-absorbable antibiotic streptomycin for 2 weeks. They were then intranasally inoculated with a non-lethal dose of SeV (2 x105 pfu). To deplete regulatory T cells (Treg), Foxp3-GFP-DTR mice were given diphtheria toxin intraperitoneally. Flow cytometry was used to quantify T cell subsets. ResultsAddition of streptomycin to the water led to a significantly increased mortality from SeV infection (81% versus 0%, n=23-26; p<0.0001). Surprisingly, the Treg number was decreased in the lung by 47% in mice given the antibiotic (streptomycin, 1.05+/-0.13 x105; n=4; versus no streptomycin, 2.0+/-0.18 x105; n=3; p=0.01). Similarly, Treg cells in the distal small intestine were decreased by 92% with streptomycin (1.57+/-1.28 x105; n=3; versus no streptomycin, 1.97+/-0.44 x106; n=3; p=0.03). To determine if reduced Tregs lead to increased mortality, Tregs were depleted in Foxp3-GFP-DTR mice, and we observed 100% mortality to SeV even in absence of streptomycin (n=4; p=0.01 versus PBS treatment). Addition of streptomycin to the water led to a significantly increased mortality from SeV infection (81% versus 0%, n=23-26; p<0.0001). Surprisingly, the Treg number was decreased in the lung by 47% in mice given the antibiotic (streptomycin, 1.05+/-0.13 x105; n=4; versus no streptomycin, 2.0+/-0.18 x105; n=3; p=0.01). Similarly, Treg cells in the distal small intestine were decreased by 92% with streptomycin (1.57+/-1.28 x105; n=3; versus no streptomycin, 1.97+/-0.44 x106; n=3; p=0.03). To determine if reduced Tregs lead to increased mortality, Tregs were depleted in Foxp3-GFP-DTR mice, and we observed 100% mortality to SeV even in absence of streptomycin (n=4; p=0.01 versus PBS treatment). ConclusionsAdministration of streptomycin markedly increased mortality to SeV and was associated with decreased Treg cells in the gastrointestinal and respiratory tracts. Even in the absence of an antibiotic, depleting Tregs led to high mortality to SeV. Tregs may link gastrointestinal and respiratory mucosal immune systems, especially in response to respiratory viral infections. Administration of streptomycin markedly increased mortality to SeV and was associated with decreased Treg cells in the gastrointestinal and respiratory tracts. Even in the absence of an antibiotic, depleting Tregs led to high mortality to SeV. Tregs may link gastrointestinal and respiratory mucosal immune systems, especially in response to respiratory viral infections.