Mast cells protect mice from Mycoplasma pneumonia.
BACKGROUND
As the smallest free-living bacteria and a frequent cause of respiratory infections, mycoplasmas are unique pathogens. Mice infected with Mycoplasma pulmonis can develop localized, life-long airway infection accompanied by persistent inflammation and remodeling.


OBJECTIVE
Because mast cells protect mice from acute septic peritonitis and gram-negative pneumonia, we hypothesized that they defend against mycoplasma infection. This study tests this hypothesis using mast cell-deficient mice.


METHODS
Responses to airway infection with M. pulmonis were compared in wild-type and mast cell-deficient Kit(W-sh)/Kit(W-sh) mice and sham-infected control mice.


RESULTS
Endpoints include mortality, body and lymph node weight, mycoplasma antibody titer, and lung mycoplasma burden and histopathology at intervals after infection. The results reveal that infected Kit(W-sh)/Kit(W-sh) mice, compared with other groups, lose more weight and are more likely to die. Live mycoplasma burden is greater in Kit(W-sh)/Kit(W-sh) than in wild-type mice at early time points. Four days after infection, the difference is 162-fold. Titers of mycoplasma-specific IgM and IgA appear earlier and rise higher in Kit(W-sh)/Kit(W-sh) mice, but antibody responses to heat-killed mycoplasma are not different compared with wild-type mice. Infected Kit(W-sh)/Kit(W-sh) mice develop larger bronchial lymph nodes and progressive pneumonia and airway occlusion with neutrophil-rich exudates, accompanied by angiogenesis and lymphangiogenesis. In wild-type mice, pneumonia and exudates are less severe, quicker to resolve, and are not associated with increased angiogenesis.


CONCLUSIONS
These findings suggest that mast cells are important for innate immune containment of and recovery from respiratory mycoplasma infection.
Xu
Xiang
X
Pulmonary and Critical Care Medicine, Mailstop 111-D, Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA 94121.
Zhang
Dongji
D
Lyubynska
Natalya
N
Wolters
Paul J
PJ
Killeen
Nigel P
NP
Baluk
Peter
P
McDonald
Donald M
DM
Hawgood
Samuel
S
Caughey
George H
GH
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D001835:Body Weight / Q000276:immunology; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D004195:Disease Models, Animal; D018450:Disease Progression; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D008168:Lung / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D008198:Lymph Nodes / Q000276:immunology / Q000473:pathology; D008407:Mast Cells / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D045803:Mycoplasma pulmonis / Q000276:immunology / Q000472:pathogenicity; D009929:Organ Size / Q000276:immunology; D011019:Pneumonia, Mycoplasma / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D037662:Pulmonary Surfactant-Associated Protein A / Q000032:analysis; D037663:Pulmonary Surfactant-Associated Protein D / Q000032:analysis; D013997:Time Factors; D015164:Vaccines, Inactivated / Q000276:immunology
D000907:Antibodies, Bacterial; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D015164:Vaccines, Inactivated