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Distribution of endosomal, lysosomal, and major histocompatability complex markers in a monocytic cell line infected
D M Ojcius1, R Hellio, A Dautry-Varsat
1Unité de Biologie des Interactions Cellulaires, CNRS URA 1960, Institut Pasteur, Paris, France. ojcius@pasteur.fr
Abstract:
The intracellular fate of Chlamydia psittaci during infection of a monocytic cell line, THP1, was characterized. Cytochalasin D inhibited phagocytosis of latex beads but had no effect on infection by C. psittaci, and vacuoles expressed the transferrin receptor, suggesting accessibility to the endocytic pathway. Early Chlamydia-containing vacuoles expressed major histocompatibility complex (MHC) class I molecules, and most vacuoles fused with host cell lysosomes, since they expressed LAMP-1 and had acidic pHs. In cells prestimulated with gamma interferon, vacuoles also expressed MHC class II molecules, suggesting that the monocytes might effectively process Chlamydia-derived antigens for presentation by MHC class I and class II molecules.
Insights
Chlamydia psittaci infects monocytes by entering the endocytic pathway. These bacteria-containing vacuoles mature and fuse with lysosomes, potentially allowing antigen presentation by major histocompatibility complex (MHC) molecules.
Area of Science:
- Microbiology
- Cell Biology
- Immunology
Background:
- Chlamydia psittaci is an obligate intracellular bacterium.
- Monocytes are key immune cells involved in host defense.
- Understanding Chlamydia's intracellular trafficking is crucial for host-pathogen interaction studies.
Purpose of the Study:
- To characterize the intracellular fate of Chlamydia psittaci within THP-1 monocytic cells.
- To investigate the involvement of the endocytic pathway in Chlamydia infection.
- To assess the potential for antigen presentation by infected monocytes.
Main Methods:
- Infection of THP-1 cells with Chlamydia psittaci.
- Use of Cytochalasin D to assess phagocytosis.
- Immunofluorescence microscopy to detect transferrin receptor, MHC class I, MHC class II, and LAMP-1.
- Measurement of vacuolar pH.
Main Results:
- Cytochalasin D inhibited latex bead phagocytosis but not Chlamydia infection.
- Chlamydia-containing vacuoles expressed the transferrin receptor, indicating endocytic pathway access.
- Vacuoles expressed MHC class I and fused with LAMP-1-positive lysosomes, becoming acidic.
- Gamma interferon stimulation led to MHC class II expression on vacuoles.
Conclusions:
- Chlamydia psittaci utilizes the endocytic pathway for entry into THP-1 cells.
- Chlamydia-containing vacuoles mature and acquire lysosomal characteristics.
- Infected monocytes, especially when activated, may present Chlamydia antigens via MHC class I and class II pathways.