FIG. 5.

Effect of an antibody against the 115-kDa serine protease on host cell invasion by early-passage L. donovani promastigotes. (A) Microscopic images of macrophages incubated with non-antibody-treated (a) or antibody-treated (b) parasites. (B) Parasites were treated with the antibody for 1 h, after which unbound antibodies were washed out, and parasites were incubated with macrophages for 24 h, 48 h, or 72 h. In another set of experiments, macrophages were pretreated with the purified protease and were then used in the macrophage invasion assay. The internalized parasites were counted after staining with Giemsa stain. Results of corresponding control experiments in which parasites were not treated with the antibody or were treated with preimmune serum are also shown. Reversal of invasion inhibition was observed for macrophages pretreated with the purified 115-kDa serine protease. Results are means ± standard deviations for four independent experiments. Asterisks indicate significance levels (*, P < 0.05; **, P < 0.01).