Complement factor H interferes with Mycobacterium bovis BCG entry into macrophages and modulates the pro-inflammatory cytokine response.
Mycobacterium tuberculosis is an accomplished intracellular pathogen, particularly within the macrophage and this is of the utmost importance in the host-pathogen stand-off observed in the granuloma during latent tuberculosis. Contact with innate immune molecules is one of the primary interactions that can occur with the pathogen M. tuberculosis once inhaled. Complement proteins may play a role in facilitating M. tuberculosis interactions with macrophages. Here, we demonstrate that factor H, a complement regulatory protein that down-regulates complement alternative pathway activation, binds directly to the model organism M. bovis BCG. Binding of factor H reaches saturation at 5-10μg of factor H/ml, well below the plasma level. C4 binding protein (C4BP) competed with factor H for binding to mycobacteria. Factor H was also found to inhibit uptake of M. bovis BCG by THP-1 macrophage cells in a dose-dependent manner. Real-time qPCR analysis showed stark differential responses of pro- and anti-inflammatory cytokines during the early stages of phagocytosis, as evident from elevated levels of TNF-α, IL-1β and IL-6, and a concomitant decrease in IL-10, TGF-β and IL-12 levels, when THP-1:BCG interaction took place in the presence of factor H. Our results suggest that factor H can interfere with mycobacterial entry into macrophages and modulate inflammatory cytokine responses, particularly during the initial stages of infection, thus affecting the extracellular survival of the pathogen. Our results offer novel insights into complement activation-independent functions of factor H during the host-pathogen interaction in tuberculosis.
Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK; Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK.
Munirah
M
Abdul-Aziz
Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK.
Anthony G
AG
Tsolaki
Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK.
Lubna
L
Kouser
Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK.
Maria V
MV
Carroll
Department of Infection and Immunity, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia.
Mohammed N
MN
Al-Ahdal
Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK; Department of Infection, Immunity and Inflammation, University of Leicester, Maurice Shock Building, University Road, Leicester, LE1 9HN, UK.
Robert B
RB
Sim
Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK. Electronic address: uday.kishore@brunel.ac.uk.
Uday
U
Kishore
D045744:Cell Line, Tumor; D050716:Complement C4b-Binding Protein / Q000276:immunology; D017242:Complement Factor H / Q000276:immunology; D016207:Cytokines / Q000235:genetics / Q000276:immunology*; D054884:Host-Pathogen Interactions; D006801:Humans; D008264:Macrophages / Q000276:immunology / Q000382:microbiology*; D009163:Mycobacterium bovis / Q000502:physiology*; D010587:Phagocytosis
C055609:C4BPA protein, human; C493495:CFH protein, human; D050716:Complement C4b-Binding Protein; D016207:Cytokines; D017242:Complement Factor H
Complement; Cytokine; Factor H; Macrophage; Mycobacterium; Phagocytosis; Tuberculosis