Pulmonary intraparenchymal leukocytes were purified from normal mice. By flow cytometry, 20-30% of the lymphocytes were positive for the expression of Mac1, a cell-surface antigen largely restricted to macrophages, neutrophils and natural killer (NK) cells. Sorted Mac1+ lung lymphocytes were large and had abundant cytoplasm with few azurophilic granules. Because Mac1+ lymphocytes did not contain any asiallo GM1+ cells, they are not likely to be NK cells. By a two-color flow cytometric analysis, Mac1+ lymphocytes were demonstrated to be TCR-αβintermediate+, TCR-γδ-, CD3intermediate+, CD4-, CD8-, Thy1-, CD5-, and B220-. These Mac1+ αβ T cells were not found in other organs such as spleen, thymus, liver, bone marrow and intestine of mice uninfected and infected with Mycobacterium bovis BCG. There was a considerable population of this unusual subset of αβ T cells in the lungs of congenitally athymic nude mice. In the Mac1+ αβ T-cell population, the proportions of Vβ8+ T cells and of forbidden T-cell clones expressing Vβ6 TCR were not much different from that in the conventional T-cell population. These results indicated that extrathymically developed αβ T cells reside in considerable proportions in the lung and that Mac1 clearly discriminates these cells from conventional ones. Interestingly, the proportion of these cells increased in the lungs of mice infected with M. bovis BCG, which raises a possibility that these cells may play some role in the host defense against mycobacterial infection.
ASJC Scopus subject areas
- Immunology and Allergy