Elevated ex vivo monocyte chemotactic protein-1 (CCL2) in pulmonary as compared with extra-pulmonary tuberculosis.
BACKGROUND
Tuberculosis causes 3 million deaths annually. The most common site of tuberculosis is pulmonary however; extra-pulmonary forms of the disease also remain prevalent. Restriction of Mycobacterium tuberculosis depends on effective recruitment and subsequent activation of T lymphocytes, mononuclear and polymorphonuclear cells to the site of infection. Tumor necrosis factor (TNF)-alpha is essential for granuloma formation and is a potent activator of monocyte chemotactic protein (MCP-1, CCL2). CCL2 is essential for recruitment of monocytes and T cells and has been shown to play a role in protection against tuberculosis. Interleukin -8 (CXCL8) is a potent activator of neutrophils. Increased levels of CCL2, CXCL8 and TNFalpha are reported in tuberculosis but their significance in different forms of tuberculosis is as yet unclear. We have used an ex vivo assay to investigate differences in immune parameters in patients with either pulmonary or extra-pulmonary tuberculosis.


METHODS
Serum levels of CCL2, CXCL8 and TNFalpha were measured in patients with pulmonary tuberculosis (N = 12), extra-pulmonary tuberculosis (N = 8) and BCG-vaccinated healthy volunteers (N = 12). Whole blood cells were stimulated with non-pathogenic Mycobacterium bovis bacille-Calmette Guerin (BCG) vaccine strain or bacterial lipopolysaccharide (LPS) and cyto/chemokines were monitored in supernatants.


RESULTS
Circulating serum levels of CXCL8 and TNFalpha were raised in all tuberculosis patients, while CCL2 levels were not. There was no difference in spontaneous cytokine secretion from whole blood cells between patients and controls. M. bovis BCG-induced ex vivo CCL2 secretion was significantly greater in pulmonary as compared with both extra-pulmonary tuberculosis patients and endemic controls. In response to LPS stimulation, patients with pulmonary tuberculosis showed increased CCL2 and TNFalpha responses as compared with the extra-pulmonary group. BCG-, and LPS-induced CXCL8 secretion was comparable between patients and controls.


CONCLUSIONS
CCL2 is activated by TNFalpha and is essential for recruitment of monocytes and T cells to the site of mycobacterial infection. Increased CCL2 activation in pulmonary tuberculosis may result in a stronger cellular response as compared with extra-pulmonary tuberculosis patients, and this may contribute to the localization of infection to the pulmonary site.
Department of Pathology and Microbiology, The Aga Khan University, Karachi, Pakistan. zahra.hasan@aku.edu
Zahra
Z
Hasan
Irfan
I
Zaidi
Bushra
B
Jamil
M Aslam
MA
Khan
Akbar
A
Kanji
Rabia
R
Hussain
D000293:Adolescent; D000328:Adult; D001500:BCG Vaccine; D001773:Blood Cells / Q000187:drug effects / Q000378:metabolism; D018932:Chemokine CCL2 / Q000097:blood* / Q000378:metabolism; D054412:Chemokine CCL8; D004731:Endotoxins / Q000494:pharmacology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018945:Monocyte Chemoattractant Proteins / Q000097:blood* / Q000378:metabolism; D009928:Organ Specificity; D014376:Tuberculosis / Q000097:blood*; D014397:Tuberculosis, Pulmonary / Q000097:blood*; D014409:Tumor Necrosis Factor-alpha / Q000032:analysis* / Q000378:metabolism
D001500:BCG Vaccine; C111835:CCL2 protein, human; C515453:CCL8 protein, human; D018932:Chemokine CCL2; D054412:Chemokine CCL8; D004731:Endotoxins; D018945:Monocyte Chemoattractant Proteins; D014409:Tumor Necrosis Factor-alpha; C044101:endotoxin, Escherichia coli