Innate immunity to bacterial infection
We are interested in understanding how antigen processing is controlled by macrophages and dendritic cells and how it may be dysregulated in autoimmune disease and subverted by pathogenic bacteria.
Our research is focused on three interrelated areas:
Control of phagosomal function
Particulate antigens and bacteria are internalized into a membrane compartment known as the phagosome that successively fuses with early and late endosomes and finally lysosomes. The behaviour of the phagosome regulates cargo degradation and bacterial killing, cytosolic export of antigen for cross-presentation and inflammasome activation. Using a variety of live cell imaging, cellular and biochemical techniques, we are examining how: signalling from Fc-gamma receptors, Toll-like receptors and scavenger receptors interact to control phagosomal function in human macrophages and dendritic cells; how ion channels and transporters modulate phagosomal pH and peri-phagosomal calcium levels to control cargo degradation and lysosomal fusion; how macro-autophagy pathways interact with phagosomes to determine functional outcomes; and how GPCRs and tyrosine kinase receptors may influence antigen processing and effector responses.
We are studying how M. tuberculosis (MTB) and non-tuberculous mycobacteria (NTM) interact with macrophages and dendritic cells, particularly: defining novel host factors controlling bacterial detection, intracellular killing and antigen presentation (through functional screening of genes identified from genetic studies); examining whether therapeutic enhancement of autophagy can be used to improve intracellular killing and how inadvertent pharmacological block of autophagy might predispose to NTM infection; examining the influence of HIV co-infection on macrophage responses to intracellular MTB (in collaboration with Dr M. Noursadeghi (UCL)); and identifying new genetic determinants controlling the pathogenesis of the NTM species M. abscessus through the combination of whole genome sequencing (in collaboration with Julian Parkhill, WTSI), in vitro functional phenotyping and clinical disease characteristics.
Together with Dr Jerry Brown (UCL), we are aiming to understand how Streptococcus pneumoniae polysaccharide capsules influences FcgR-dependent and independent uptake and subsequent antigen processing.
Bryant, J.M., Grogono, D. M., Greaves, D., Foweraker, J., Roddick, I., Inns, T., Reacher,M. Haworth, C.S., Curran, M.D., Harris, S.R., Peacock, S.J., Parkhill, J. and Floto, R.A. Whole-genome sequencing to identify transmission of Mycobacterium abscessus between patients with cystic fibrosis: a retrospective cohort study. Lancet 381, 1551–1560 (2013).
Renna, M., Schaffner, C., Brown, K., Shang, S., Tamayo, M. H., Hegyi, K., Grimsey, N. J., Cusens, D., Coulter, S., Cooper, J., Bowden, A. R., Newton, S. M., Kampmann, B., Helm, J., Jones, A., Haworth, C. S., Basaraba, R. J., DeGroote, M. A., Ordway, D. J., Rubinsztein, D. C. and Floto, R. A. Azithromycin blocks autophagy and may predispose cystic fibrosis patients to mycobacterial infection. J. Clin. Invest. 121, 3554–3563 (2011).
Williams, A., Sarkar, S., Cuddon, P., Ttofi, E. K., Saiki, S., Siddiqi, F. H., Jahreiss, L., Fleming, A., Pask, D., Goldsmith, P., O'Kane, C. J., Floto, R. A. & Rubinsztein, D. C. Novel targets for Huntington's disease in an mTOR-independent autophagy pathway. Nature Chem. Biol. 4, 295–305 (2008).
Floto, R.A., Sarkar, S, Perlstein, E.O., Kampmann, B., Schreiber, S.L. & Rubinsztein, D.C. Small molecule enhancers of rapamycin-induced TOR inhibition promote autophagy, reduce toxicity in Huntington’s disease models and enhance killing of mycobacteria by macrophages. Autophagy 3, 620–622 (2007).
Clatworthy, M.R., Willcocks, L., Urban, B.,Langhorne, J., Williams, T., Watkins, N.A., Rankin, A., Floto, R.A. & Smith, K.G.C. SLE-associated defects in the inhibitory receptor FcgRIIb reduce susceptibility to malaria. Proc Natl Acad Sci USA 104, 7169–7174 (2007).
Floto, R.A., MacAry, P.A., Boname, J.M., Mien, T.S., Houben, E.N.G., Pieters, J., Day, C., Oehlmann, W., Singh, M., Smith, K.G.C. & Lehner, P.J. Dendritic cell stimulation by mycobacterial HSP70 is mediated through the HIV co-receptor CCR5. Science 314, 454–458 (2006).
Floto, R.A., Clatworthy, M.R., Heilbronn, K.R., Rosner, D.R., MacAry, P.A., Rankin, A., Lehner, P.J., Ouwehand, W.H., Allen, J.M., Watkins, N.A. & Smith, K.G.C (2005). An SLE-associated polymorphism of the inhibitory receptor FcgRIIb excludes it from lipid rafts and leads to loss of function. Nature Med. 11, 1056–1058 (2005).