Role of gamma delta T cells in immunopathology of pulmonary Mycobacterium avium infection in mice

Abstract

Several studies have shown that gamma delta T cells influence granuloma development after infection with intracellular pathogens. The role of gamma delta T cells in controlling the influx of inflammatory cells into the lung after Mycobacterium avium infection was therefore examined with gene-disrupted mice (K/O). The mice were infected with either M. avium 724, a progressively replicating highly virulent strain of M. avium, or with M. avium 2-151 SmT, a virulent strain that induces a chronic infection. gamma delta-K/O mice infected with M. avium 2-151 SmT showed early enhanced bacterial growth within the lung compared to the wild-type mice, although granuloma formation was similar in both strains. gamma delta-K/O mice infected with M. avium 724 showed identical bacterial growth within the lung compared to the wild-type mice, but they developed more-compact lymphocytic granulomas and did not show the extensive neutrophil influx and widespread tissue necrosis seen in wild-type mice. These data support the hypothesis that isolates of M. avium that induce protective T-cell-specific immunity are largely unaffected by the absence of gammadelta T cells. Whereas with bacterial strains that induce poor protective immunity, the absence of gamma delta T cells led to significant reductions in both the influx of neutrophils and tissue damage within the lungs of infected mice.

FIG. 1

Bacterial growth in γδ-K/O mice infected with M. avium 724 or 2-151 SmT. γδ-K/O mice and their wild-type littermate controls were infected with approximately 500 bacilli via aerosol. Bacterial load was assessed up to 120 days postinfection. Data are expressed as the mean ± the standard deviation (n = 4). ∗, P < 0.05.

FIG. 2

Representative low-magnification photomicrographs of lung tissue from wild-type and γδ-K/O mice infected with M. avium 724. (A) Wild-type mice at 60 days postinfection. Note the limited cellular infiltrates composed of scattered lymphocyte foci, including apparent bronchial alveolar lymphatic tissue expansion. The lungs of γδ-K/O mice were similar in appearance at this time point. (B) γδ-K/O mice at 90 days postinfection. There are multiple small granulomas composed predominantly of macrophages and lymphocytes with few neutrophils. (C) Wild-type mice at 90 days postinfection. A large focus of necrosis with central caseation can be seen, with lesions surrounded by neutrophils and then cuffed with macrophages (enlarged in Fig. 3). (D) γδ-K/O mice at 120 days postinfection. Large granulomatous lesions composed primarily of macrophages with a few foci of neutrophils are evident. Lymphocyte numbers appear to have waned since day 90. Hematoxylin and eosin staining was used. Bar, 100 μm.

FIG. 3

Representative high-magnification photomicrograph of lung tissue from mice infected with M. avium 724. (A) Section of a caseated lesion in a wild-type mouse at 90 days postinfection. Note the concentrated laminated rings of degenerative neutrophils (middle) and epithelioid macrophages (top) surrounding the central caseation (bottom). The thick-bar area is magnified in panel B; the thin-bar area is magnified in panel C. (B) Higher magnification of the neutrophilic lamina (bottom) with the epithelioid macrophages (top). (C) The center of the caseated area contains amorphous debris. (D) Acid-fast bacilli in macrophages. This is a magnification of the area of panel A just above the thick bar. (E) Section of a noncaseated lesion in a γδ-K/O mouse at 90 days postinfection. Note that the lesion is composed primarily of macrophages and lymphocytes. (F) Acid-fast bacilli in macrophages from a γδ-K/O mouse at 90 days postinfection. The panel is a magnification from an area similar to that shown in panel E. Panels A, B, C, and E were stained with hematoxylin and eosin; panels D and F were stained with Kinyoun’s stain. Bar, 10 μm.

FIG. 4

Representative moderate-magnification photomicrograph of liver tissue from M. avium 724-infected mice. (A) Wild-type mice at 120 days postinfection. Cellular infiltrates resulting in the formation of multifocal granulomatous hepatitis are shown. (B) γδ-K/O mice at 120 days postinfection. This image is similar to panel A, with cellular infiltrates resulting in the formation of multifocal granulomatous hepatitis. Panels were stained with hematoxylin and eosin. Bar, 100 μm.

FIG. 5

Representative low-magnification photomicrographs of lung tissue from M. avium 2-151 SmT-infected mice. (A) Wild-type mice at 60 days postinfection. Cellular infiltrates resulting in the formation of primary granulomas composed predominantly of macrophages with few lymphocytes are shown. This response was prominent earlier than the one shown in Fig. 2. (B) γδ-K/O mice at 60 days postinfection. The lesions are similar to those in Fig. 4A, but the proportion of lymphocytes is higher than in the wild type. (C) Wild-type mice at 90 days postinfection. The lymphocytic granulomas are larger than at 60 days postinfection (Fig. 4A). (D) γδ-K/O mice at 90 days postinfection. The γδ K/O mice also showed an increase in granuloma formation. These are composed predominantly of macrophages and lymphocytes, with the proportion of lymphocytes being higher than in the wild type (Fig. 4C). Panels were stained with hematoxylin and eosin. Bar, 100 μm.