The half-time for the degradation of horseradish peroxidase (HRP) is increased from 14 h to 37 h in Con A-treated cells, while the half-time for the degradation of [125I]BSA is increased from 5.4 h to 14.8 h. This supports prior microscopic observations which suggested that Con A pinosomes showed a marked impairment in their ability to form phagolysosomes. Artifacts due to anomalous behavior of HRP-Con A complexes, or to inhibition of lysosomal hydrolases by Con A, could be excluded.
These indications of impaired phagolysosome formation, as well as those described in the preceding paper, could be reversed by postincubation of the cells in mannose, but not in galactose. This reversal is accompanied by a dissociation of Con A-FITC from the inner surface of the pinosome membrane, into the vesicle contents. These observations may be relevant to the ability of Con A to affect several membrane characteristics, and are also of interest in relation to the impaired formation of phagolysosomes which has been described in certain in vitro parasitic infections of macrophages or other cells.