Adherence and phagocytosis of yeast cells by blood monocytes effects in vitro of a therapeutic doxycycline concentration

The effect of a therapeutic doxycyline concentration on yeast-cell phagocytosis by blood monocytes was studied in vitro by means of a fluoresence assay. This method allows discrimination between monocyte-adherent yeast cells and ingested yeast cells. The adhesive and phagocytic capacity of 50 monocytes was measured in 16 healthy donors. Yeast-cell adherence was not influenced by doxycycline. In contrast, a slight depression of phagocytosis by doxycycline was suggested. The median difference between doxycyclin-treated and control monocytes was 30% (p = 0.07). It is reasonable to assume that a possible inhibitory effect of doxycycline on monocyte phagocytosis is negligible in healthy individuals. However, a clinically significant effect cannot be excluded in severely immuno-compromised patients.