Late endocytic multivesicular bodies intersect the chlamydial inclusion in the absence of CD63

Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO. 63110, USA

^* To whom correspondence should be addressed. Email: beatty{at}borcim.wustl.edu.

	Abstract

Chlamydiae are obligate intracellular bacterial pathogens that replicate solely within a membrane-bound vacuole termed an inclusion. Within the confines of the inclusion, the replicating bacteria acquire amino acids, nucleotides, and other precursors from the host cell. Trafficking from CD63-positive multivesicular bodies to the inclusion was previously identified as a novel interaction providing essential precursors for maintenance of a productive intracellular infection. The present study analyzes the direct delivery of resident protein and lipid constituents of multivesicular bodies to the intracellular chlamydiae. Manipulation of this trafficking pathway with an inhibitor of multivesicular body transport and delivery of exogenous antibodies altered protein and cholesterol acquisition, and delayed the maturation of the chlamydial inclusion. Although inhibitor studies and ultrastructural analyses confirmed a novel interaction between CD63-positive multivesicular bodies and the intracellular Chlamydia, neutralization with small interfering RNAs and anti-CD63 Fab fragments revealed that CD63 itself was not required for this association. These studies confirm CD63 as a constituent in multivesicular body-to-inclusion transport, however, other requisite components of these host cell compartments must control the delivery of key nutrients essential to intracellular bacterial development.