Local cell recruitment and cytokine production following intradermal injection with Microsporum canis antigen in cats

Eight cats that had recovered from experimental Micosporum cansis infection were injected intradermally with a soluble M. cansis antigen preparation (SMCA) and saline (control). All cats received both SMCA and saline injections. Injection sites were scored for gross inflammation at 30 min, 24, 48 and 72 h after injection and skin biopsy specimens from these sites were taken at 48 h (four cats) and 72 h (the other four cats) after injection. Tissue sections were stained using haematoxylin and eosin (H&E or labelled immunohistochemically using antibodies specific for major histocompatibility complex (MHC) class II, macrophages and polymorphonucear leucocytes, B-cells and T-cell subjects (CD4, CD8). The number of labelled cells of each type in the inflammatory infiltrate was graded. Tissue biopsies were assayed using semiquantitive reverse transcription-polymerase chain reaction to detect mRNA for gamma-interferon (IFN-gamma), interleukin-4 (IL-4), IL-10 and IL-12p40.

All of the SMCA injection sites had evidence of gross inflammation at all time points after 30 min, whereas the control sites did not. At 48 h after injection, eosinophils and mast cells predominated in the infiltrate, whereas at 72 h after injection, lymphocytes and macrophages predominated. There were very few plasma or beta-cells in any sections. Peak numbers of macrophages were seen 48 h after injection, whereas peak numbers of cells expressing MHC class II or CD3 were seen 72 h after injection. mRNA for IFN-gamma, IL-10 and IL-12p40 was detected in both SMCA and control skin biopsy specimens. mRNA for IL-4 was not detected.

This study showed that intradermal injection of SMCA induces a delayed-type hypersensitivity response in cats that have recovered from M. canis infection.