Centre for Molecular Medicine


Research Groups

Inflammatory Bowel Disease

Professor AW Segal

Inflammatory Bowel Disease (IBD)

IBD, which affects approximately 1 in 500 of the population, is a generic term that includes Crohn's disease (CD) and ulcerative colitis (UC). However, some very significant differences in the inflammatory response in these two conditions seem to reflect the underlying mechanisms of the two diseases.

Recently we have shown major abnormalities in the inflammatory response to bacteria in these two conditions. Whereas, UC is characterised by prolonged inflammation due to a defective resolution phase, CD results from impaired acute inflammation. Macrophages are grossly abnormal in these two conditions and play a central role in disease progression. We are currently investigating the precise mechanisms that fail in CD and UC. In CD it appears to involve the secretory machinery required for pro-inflammatory cytokine release. In UC the problem appears to involve a signalling system that normally switches on the production and release of resolving mediators. Acute inflammation is normally only switched on for about 24 hours. This suppression does not occur, or is delayed, in UC. We are currently investigating the signalling pathways normally activated in macrophages by bacteria and then determine where they are defective in UC cells. These approaches should greatly increase our knowledge of these two chronic inflammatory diseases and facilitate the development of rational treatment.

IBD is approximately 4 times more common in the Jewish population. The reasons for this are not entirely understood; it is thought that genetic factors contribute. With a view to further our understanding of this we have undertaken a large genetic study on Ashkenazi Jews with familial or sporadic Crohn's disease.  We have identified causal genes in the form of CSF2RB and LRRK2 in addition to the well-recognised NOD2.

Major reviews of the causes of Crohn's disease by Professor Segal are:
F1000 Research; "Making sense of the cause of Crohn's - a new look at an old disease" https://f1000research.com/articles/5-2510/v1

J Intern Med. Studies on patients establish Crohn's disease as a manifestation of impaired innate immunity. https://www.ncbi.nlm.nih.gov/pubmed/?term=segal+aw+journal+of+internal+m...

Other References

1. Defective acute inflammation in Crohn's disease: a clinical investigation.
Marks DJ, Harbord MW, MacAllister R, Rahman FZ, Young J, Al-Lazikani B, Lees W, Novelli M, Bloom S, Segal AW. 
Lancet 2006;367:668-678.

2. Disordered macrophage cytokine secretion underlies impaired acute inflammation and bacterial clearance in Crohn's disease.
Smith AM, Rahman FZ, Hayee B, Graham SJ, Marks DJ, Sewell GW, Palmer CD, Wilde J, Foxwell BM, Gloger IS, Sweeting T, Marsh M, Walker AP, Bloom SL, Segal AW.
J Exp Med 2009;206:1883-1897.

3. A New Look at Familial Risk of Inflammatory Bowel Disease in the Ashkenazi Jewish Population.
Schiff ER et al. Dig Dis Sci. 2018 Nov;63(11):3049-3057.

4. Rare coding variant analysis in a large cohort of Ashkenazi Jewish families with inflammatory bowel disease. 
Schiff ER et al. Hum Genet. 2018 Sep;137(9):723-734

5. Insights into the genetic epidemiology of Crohn's and rare diseases in the Ashkenazi Jewish population. 
Rivas MA et al.  PLoS Genet. 2018 May 24;14(5):e1007329. doi:
6. Functional variants in the LRRK2 gene confer shared effects on risk for Crohn's disease and Parkinson's disease. 
Hui KY et al. Sci Transl Med. 2018 Jan 10;10(423). pii: eaai7795. doi: 10.1126/scitranslmed.aai7795.

7. Genetic Complexity of Crohn's Disease in Two Large Ashkenazi Jewish Families. 
Levine AP et al.  Gastroenterology. 2016 Oct;151(4):698-709. doi: 0.1053/j.gastro.2016.06.040.

Cell biology of phagocytes

Professor A.W. Segal

NADPH oxidase, cytoskeleton, oxygen radicals, killing/digestion of microbes

Professor Segal and colleagues discovered and characterised the NADPH oxidase of phagocytes and demonstrated how defects in this system cause Chronic Granulomatous Disease (CDG). 

Phagocytes and in particular neutrophils constitute the first line of defence of the innate immune system against invading pathogens. These white blood cells are able to chase, bind and finally engulf bacteria in a sealed phagocytic vacuole formed by invagination of the plasma membrane. Within this specialised organelle, pathogens are exposed to proteolytic enzymes that are downloaded from cytoplasmic granules. Setting ionic conditions and pH within the vacuole that are optimal for the activity of these enzymes is critical for an efficient killing and digestion of the pathogen. The NADPH oxidase, as well as a range of ion channels, ion exchangers and ion pumps contribute the optimisation of the vacuolar environment. We used a range of electrophysiological, imaging, spectroscopy and knock-out mouse experiments to delineate the respective role of proteases and reactive oxygen species in the killing process.

We have found that the pH in the phagocytic vacuole of neutrophils becomes very alkaline as a consequence of the action of the NADPH oxidase, reaching approximately pH 9.0, which is optimal for the activity of the major neutral proteases, cathepsin G and elastase that are released into the vacuole from the cytoplasmic granules.

More recently we have examined the pH within the phagocytic vacuoles of the mononuclear phagocyte cells. An unexpected observation was the striking difference in phagosomal environment between the three monocytes subsets. Classical monocytes and neutrophils exhibited alkaline phagosomes, non-classical monocytes had more acidic phagosomes, while intermediate monocytes had a phenotype in-between. We next investigated the differences between primary naïve dendritic cells (DCs) vs. in vitro monocyte-derived DCs (MoDC) and established that both these cells had acidic phagosomal environments. Across all phagocytes, alkalinisation was dependent upon the activity of the NADPH oxidase.


1. Novel cytochrome b system in phagocytic vacuoles of human granulocytes.
Segal AW, Jones OT. Nature. 1978 Nov 30;276(5687):515-7.

2. Absence of a newly described cytochrome b from neutrophils of patients with chronic granulomatous disease.
Segal AW, Jones OT, Webster D, Allison AC. Lancet. 1978 Aug 26;2(8087):446-9

3. The respiratory burst of phagocytic cells is associated with a rise in vacuolar pH.
Segal AW, Geisow M, Garcia R, Harper A, Miller R. Nature. 1981 Apr 2;290(5805):406-9

4. Killing activity of neutrophils is mediated through activation of proteases by K+ flux.
Reeves EP, Lu H, Jacobs HL, Messina CG, Bolsover S, Gabella G, Potma EO, Warley A, Roes J, Segal AW. Nature. 2002 Mar 21;416(6878):291-7.

5. Alkalinity of neutrophil phagocytic vacuoles is modulated by HVCN1 and has consequences for myeloperoxidase activity.
Levine AP, Duchen MR, de Villiers S, Rich PR, Segal AW. PLoS One. 2015 Apr 17;10(4):e0125906.

6. The NADPH Oxidase and Microbial Killing by Neutrophils, With a Particular Emphasis on the Proposed Antimicrobial Role of Myeloperoxidase within the Phagocytic Vacuole.
Levine AP, Segal AW. Microbiol Spectr. 2016 Aug;4(4). doi: 10.1128/microbiolspec.

7. Variations in the Phagosomal Environment of Human Neutrophils and Mononuclear Phagocyte Subsets.
Foote JR, Patel AA, Yona S, Segal AW. Front Immunol. 2019 Mar 1;10:188. doi: 10.3389/fimmu.2019.00188. 

8. How neutrophils kill microbes. 
Segal AW. Annu. Rev. Immunol. 2005; 23:197.