Glycogen autophagosomes in polymorphonuclear leukocytes induced by rickettsiae

Abstract

Guinea pig polymorphonuclear leukocytes (PMNs), rich in glycogen granules, were collected from sodium-caseinate-induced peritoneal exudate. When these cells were incubated with rickettsiae, many microorganisms were phagocytized within 30 minutes at 35 degrees C and vacuoles up to 5 microns in diameter containing glycogen granules were present. Contained within these vacuoles were phagocytized extracellular material and a dense, lysosomelike substance that was acid phosphatase positive. These vacuoles, which were interpreted to be autophagosomes, were absent from PMNs that had not been stimulated with microorganisms. The number of rickettsiae in the PMN did not appear to be related to the number of autophagosomes. About 8% and 80% of thin-sectioned profiles of PMNs contained these vacuoles after 30 minutes and 4 hours incubation, respectively. After 4 hours, the PMNs contained multiple autophagosomes. Almost all of the glycogen granules were in autophagosomes in some of the cells. In some PMNs, discontinuous membranes encircled some glycogen. When PMNs were initially incubated with thorium dioxide and ferritin, and extensively washed prior to incubation with rickettsiae, glycogen was found surrounded by flattened secondary lysosomes containing the dense tracers. Some autophagosomes also contained the electron-dense tracers. These results suggest that rickettsiae induce the rapid formation of glycogen-containing autophagosomes in guinea pig peritoneal PMNs in vitro.