Distribution of Leucocyte Subsets in Bronchial Mucosa from Dogs with Eosinophilic Bronchopneumopathy

Immunohistochemistry was used to characterize the distribution of leucocyte subsets in the bronchial mucosa of 11 dogs with idiopathic eosinophilic bronchopneumopathy (EBP). Formalin-fixed tissues from all dogs were included in the study, but frozen tissue from only one dog was available. MHC class II+ cells were found in moderate numbers in the lamina propria (LP). These cells were morphologically either dendritic-like cells or macrophages, but many macrophages did not express MHC class II. Such molecules were expressed by occasional fibroblasts. L1+ cells, which formed a relatively small component of the LP inflammatory infiltrate, were morphologically either macrophages or polymorphonuclear cells (probably eosinophils). IgA+ plasma cells were found in varying numbers in the LP, mostly in association with glandular tissue. IgG+ plasma cells were less common, and IgM+ plasma cells were present in low numbers. Many CD3+ cells were present in the LP. In the single case from which frozen tissue was available, most of the lymphocytes were labelled with CD4 marker, while smaller numbers were CD8+ T cells. Most of the lymphocytes in this case were positively labelled with T-cell receptor (TCR)-αβ marker. TCR-γδ+ cells, although less common, were present in significant numbers throughout the LP. CDlc+ dendritic cells were numerous in the epithelium and in the LP, immediately beneath the basement membrane. These findings, which were similar to those described in human asthma, are suggestive of a Th2 dominant immune response in canine EBP. As in human asthma, this provides a possible basis for new forms of treatment in canine EBP.