Increase of γδ T lymphocytes in murine lungs occurs during recovery from pulmonary infection by Nocardia asteroides

Previous studies have demonstrated that gamma delta T lymphocytes are important for host resistance to pulmonary infection of the murine lung by log-phase cells of Nocardia asteroides. To study the role of gamma delta T cells in nocardial interactions in the murine lung, C57BL/6J wild type and C57BL/6J-Tcrd (gamma delta T-cell knockout mice) were infected intranasally with log-phase cells of N. asteroides GUH-2. At 3, 5, and 7 days after infection, the gamma delta T cells were quantified by multiparameter flow cytometry. At the same time, Gram and hematoxylin-eosin stains of paraffin sections were performed to monitor the host responses. The data showed that gamma delta T lymphocytes increased significantly within the lungs after intranasal infection, and the peak of this cellular increase occurred at 5 days. Furthermore, at this time, greater than 50% of the CD3 T-cell receptor (TCR)-positive (CD3(+)) cells were gamma delta TCR positive. Histological examination clearly showed divergent inflammatory responses in the lungs of wild-type mice compared to gamma delta T-cell knockout mice. The C57BL/6J-Tcrd mice were less capable of clearing the organism, and the polymorphonuclear leukocyte response lasted longer than in wild-type C57BL/6J mice. These results showed that gamma delta T cells were actively involved in modulating the innate host responses to murine pulmonary infection by N. asteroides.