Introduction

Upper respiratory tract aspergillosis (URTA) is an invasive disease of apparently immunocompetent cats. A predominantly Th1 immune response is required to clear fungal infections. Purebred brachycephalic cats have been shown to be predisposed to infection, suggesting that their conformation and/or a defect in their innate immunity permits fungal colonization and invasion.

Objectives

To describe the leukocyte population of the nasal mucosa in cats with URTA.

Methods

Sinonasal mucosal samples from cats with URTA (n=6) and control cats (n=6) were stained with H&E, and immunohistochemistry was performed for identification of T lymphocytes (CD3), B lymphocytes (CD79b), myelomonocytes (MAC387), antigen-presenting cells (MHCII), and plasma cells (IgA, IgG, and IgM). Digital images of sections were captured using an Axio Scan.Z1, and the number of positively labeled cells was determined for selected lengths of epithelium (cells/mm) and areas of lamina propria (cells/mm²).

Results

Inflammation of the nasal mucosa was present, in variable degrees, in all cats with URTA but was absent in all control cats. Affected cats had significantly greater numbers of epithelial lymphocytes, IgG+ cells, CD79+ cells, and MAC387+ cells. Ig+ and IgG+ cells were also present in greater numbers in the lamina propria of URTA cats compared to the controls.

Conclusions

The leukocyte population of the sinonasal mucosa in cats with URTA is highly variable, but does not appear consistent with a predominantly Th1 immune response. Characterisation of mucosal leukocyte function and cytokine expression is required to fully elucidate the mucosal immune response to feline URTA.