Humoral and cellular immune responses to Microsporum canis in naturally occurring feline dermatophytosis.

Peripheral blood lymphocytes isolated from cattery cats which were culture positive for Microsporum canis, or from cats which had recovered from M. canis infection, showed a significantly greater mean in vitro blastogenic response to M. canis antigen than lymphocytes from uninfected cats. Mean lymphocyte reactivity to concanavalin A was higher in cats which had recovered from infection than in either culture positive or uninfected cats, whereas reactivity to phytohemagglutinin was highest in the culture positive group. Antibody (both IgG and IgM) against dermatophyte glycoprotein antigen was detectable in the plasma of all cats, but was present in significantly higher titres in the culture positive group. Our results demonstrate that M. canis infected cats mount strong humoral and cellular immune responses to the organism; these responses can be detected by use of anti-dermatophyte antibody quantitation and lymphocyte blastogenesis assays, as has been reported previously for dermatophytosis in other species. Asymptomatic, culture positive cats were found in only three of seven catteries and were genetically related, raising the possibility of genetic predisposition to persisting asymptomatic infection.