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The CD14 receptor does not mediate entry of Mycobacterium tuberculosis into human mononuclear phagocytes
Homayoun Shams1, Benjamin Wizel, David L Lakey
1Center for Pulmonary and Infectious Disease Control, University of Texas Health Center, 11937 U.S. Highway 271, Tyler, TX 75708-3154, USA.
Abstract:
Prior reports have suggested that CD14 mediates uptake of Mycobacterium tuberculosis into porcine alveolar macrophages and human fetal microglia, but the contribution of CD14 to cell entry in human macrophages has not been studied. To address this question, we used flow cytometry to quantify uptake by human monocytes and alveolar macrophages of M. tuberculosis expressing green fluorescent protein. Neutralizing anti-CD14 antibodies did not affect bacillary uptake and the efficiency of bacillary entry was similar in THP-1 cells expressing low and high levels of CD14. However, most internalized bacteria were found in CD14+ but not in CD14- monocytes because M. tuberculosis infection upregulated CD14 expression. We conclude that: (1) CD14 does not mediate cellular entry by M. tuberculosis; (2) M. tuberculosis infection upregulates CD14 expression on mononuclear phagocytes, and this may facilitate the pathogen's capacity to modulate the immune response.
Insights
CD14 does not mediate Mycobacterium tuberculosis entry into human cells. However, M. tuberculosis infection increases CD14 expression on immune cells, potentially aiding immune response modulation.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Previous studies suggested CD14 mediates Mycobacterium tuberculosis (M. tuberculosis) uptake in porcine alveolar macrophages and human fetal microglia.
- The role of CD14 in M. tuberculosis entry into human macrophages remained uninvestigated.
Purpose of the Study:
- To investigate the contribution of CD14 to M. tuberculosis cellular entry in human monocytes and alveolar macrophages.
- To determine if CD14 expression levels affect M. tuberculosis uptake efficiency.
Main Methods:
- Utilized flow cytometry to quantify M. tuberculosis uptake in human monocytes and alveolar macrophages.
- Employed neutralizing anti-CD14 antibodies to assess CD14's role in bacterial entry.
- Compared M. tuberculosis uptake in THP-1 cells with varying CD14 expression levels.
Main Results:
- Neutralizing anti-CD14 antibodies did not inhibit M. tuberculosis uptake.
- M. tuberculosis entry efficiency was comparable in THP-1 cells with low and high CD14 expression.
- The majority of internalized M. tuberculosis were found in CD14+ monocytes, as infection upregulated CD14 expression.
Conclusions:
- CD14 is not a mediator of M. tuberculosis cellular entry.
- M. tuberculosis infection upregulates CD14 expression on mononuclear phagocytes.
- Upregulated CD14 may enhance M. tuberculosis's ability to modulate the host immune response.