Effect of antibody on entry of Rickettsia tsutsugamushi into polymorphonuclear leukocyte cytoplasm

The effects of rickettsial antibodies on the entry of Rickettsia tsutsugamushi, Gilliam strain, into guinea pig polymorphonuclear leukocyte cytoplasm were studied by electron microscopy. Immunoglobulin G fractions were obtained from four rabbit antisera against: yolk sac-propagated rickettsiae; baby hamster kidney cell (BHK-21)-propagated rickettsiae; formaldehyde-fixed, BHK-21 cell-propagated rickettsiae; and glutaraldehyde-fixed, BHK-21 cell-propagated rickettsiae. A fuzzy coating was observed on the rickettsiae after reaction with each of the antibodies. All of the antibodies increased the uptake of rickettsiae by polymorphonuclear leukocytes. The opsonization effect was higher with an antibody against BHK-21 cell-propagated rickettsiae than with an antibody against yolk sac-propagated rickettsiae, and an antibody to live rickettsiae had a higher opsonization effect than did antibodies to chemically fixed rickettsiae. Rickettsiae were released from phagosomes into the cytoplasm with the four antibodies. The highest number of rickettsiae were released into the cytoplasm with antibody against live rickettsiae propagated in BHK-21 cells. The four antibodies inhibited the translocation of the cytoplasmic rickettsiae from the filamentous area to glycogen-rich zones. Almost 100% inhibition of translocation was observed with antibodies against live rickettsiae. These results indicate that rabbit antibodies against rickettsiae, when used alone, were unable to completely prevent rickettsial entry into polymorphonuclear leukocyte cytoplasm in vitro.