Detection of Aspergillus-specific Immunoglobulin A in Cats with Upper Respiratory Aspergillosis

Abstract

Background- Severe mycotic infection in humans is often associated with host immune impairment. Feline upper respiratory aspergillosis (URTA) is an emerging mycosis with worldwide distribution and currently the pathogenesis is poorly understood. Characterisation of the humoral immune response in feline URTA will assess whether selective immunodeficiency underlies susceptibility and will determine the utility of class-specific antibody detection for diagnosis. Aims- To determine whether serum Aspergillus-specific IgA and Aspergillus-specific IgM can be detected in cats with URTA by enzyme linked immunoassay (ELISA), and to evaluate the diagnostic utility of IgA and IgM detection alone, or in combination with Aspergillus-specific IgG detection. Animals- Twenty-three cats with confirmed URTA (Group 1 cases), 32 cats with upper respiratory disease without aspergillosis (Group 2 respiratory controls) and 84 non-respiratory controls (Group 3 non-respiratory controls). Methods- Indirect ELISA was optimised and used to detect serum Aspergillus-specific IgA. ELISA for detection of Aspergillus-specific IgM could not be optimised. Optimal cut-off were determined by receiver-operating curve analysis. Sensitivity (Se) and specificity (Sp) for diagnosis were determined using IgA alone and in combination with IgG. Results- Serum IgA was detected in 91.3% of Group 1 cats. At a cut-off value of 71.9 ELISA units (EU)/mL the Se of IgA detection was 78.3% and Sp was highest for Group 2 controls (96.9%). Se for IgG was 100% and Sp was 92.2%. Using combined IgA and IgG results at cut-offs optimised for Sp for IgA and Se for IgG and combined controls (Groups 2 and 3), Se was 100% and Sp was 85.3%. Conclusion and clinical importance- Aspergillus-specific IgA can be detected by ELISA in the majority of affected cats with URTA and primary IgA deficiency is not a feature. Paired measurement of serum Aspergillus-specific IgA and IgG demonstrated no benefit for diagnosis of URTA over IgG alone. Further work is needed to determine Aspergillus-specific IgM in affected cats with URTA.