The effect of canine macrophages on the adherence and growth of Blastomyces dermatitidis yeast: evidence of a soluble factor that enhances the growth of B. dermatitidis yeast.

Blastomycosis is a medically important systemic fungal infection of dogs and humans. Phagocytic cells are the first line of cellular defence against B. dermatitidis, and are a prominent feature in the lesions and exudate of canine blastomycosis. The adherence of B. dermatitidis yeast to canine phagocytes, and the effects of such adherence on the growth of B. dermatitidis yeast, has not been previously reported. The results of this study demonstrate that canine complement enhances the adherence of B. dermatitidis yeast to canine macrophages. Initiation of the canine complement cascade by B. dermatitidis yeast appeared to occur predominantly by the classical pathway. Adherence of B. dermatitidis yeast to canine macrophages enhanced the growth of the yeast. In the absence of macrophages, this effect could be duplicated by incubating yeast in conditioned medium from co-cultures of macrophages and yeast. This observation suggests that a soluble factor is involved in the growth enhancement of the yeast, These findings provide new insights into the adherence of B. dermatitidis yeast to canine macrophages, and how adherence influences the proliferation of B. dermatitidis yeast.