Enzymes in immune cells play an important role in host defense against tuberculosis

BIRMINGHAM, Ala. – Using lung tissue that has just been resected from 21 patients and two different mouse models, tuberculosis researchers at the University of Alabama at Birmingham and the Africa Health Research Institute, or AHRI, have identified proteins that play an important role in host defense. fight this deadly disease.

The study was led by Andries "Adrie" Steyn, Ph.D., a UAB microbiology professor who manages laboratories at UAB and AHRI, in Durban, South Africa. Because tuberculosis rates are very high, or TB, in South Africa, infected human lung tissue is available from the nearest hospital, because patients undergo surgery as the last hope for recovery.

Studies directly from microanatomic niches in fresh lung tissue – including healthy and very sick areas – can then reveal differences in immune responses and cell activity in these different regions. Steyn and his research team said this unique approach would help in identifying potential host factors that could be targeted therapeutically to limit the extensive tissue damage associated with chronic pulmonary TB disease. This dangerous lung tissue, including the lungs infected with various drug-resistant or widely resistant TB bacteria, is handled carefully in AHRI's sophisticated biosafety laboratory because at least one to three TB bacteria are in aerosol droplets can cause infection. TB infection by the bacteria Mycobacterium tuberculosis, or Mtb, kills around 1.3 million people per year.

Steyn and colleagues were able to separate various types of cells found in special recesses of newly resected TB lungs and characterize these cells for the production of heme oxygenase-1 protein. Heme oxygenase-1, or HO-1, is an enzyme that protects cells from harmful reactive oxygen or nitrogen intermediates; HO-1 is also able to control the inflammatory response.

The researchers found that HO-1 in pulmonary human TB was expressed primarily by myeloid immune cells, including neutrophils and macrophages, and the level of HO-1 in these cells was directly proportional to the protection of TB pathophysiology.

In particular, there is a greater percentage of HO-1-producing neutrophils and macrophages in the uninfected area of ​​the lung than in the affected area, and cells in the uninfected area produce more HO-1 than cells in the area sick. As a result, the lack of HO-1 protection in the diseased area allows the production of myeloid cells from reactive oxygen reactive and nitrogen species. What makes this finding clinically relevant is that HO-1 is very important in humans but not in mice, which shows the importance of examining the lung tissue of human TB to complement animal models for TB.

"To my knowledge, extensive analysis of lung tissue of newly resected pulmonary TB is the first of its kind, because the lungs are rare," said Steyn.

These findings in humans supported by two models of HO-1 deficient mice showing HO-1 are needed to control cell infiltration and myeloid cell infiltration to protect against TB development. One mouse model is a global knockout of the HO-1 gene; the other model is HO-1 knockout only on myeloid cells. In both models, knockout mice had a greater susceptibility to Mtb infection – knockout mice died faster and had higher Mtb loads in the lungs and spleen. KO rats also experience increased immune cell infiltration and cytokine levels, cell signaling proteins that regulate or stimulate the immune response.

Overall, findings from the human lungs and mouse models suggest that HO-1 expression, especially in myeloid cells, seems important for host defense against the development of Mtb disease. For TB patients in humans, Steyn said, research shows that finding ways to increase HO-1 activity might limit immunopathology during active TB.

The research was published on November 13 in the journal Cell Report, and also displayed on the front cover of the journal.

Two laboratories, a separate world

Steyn is the principal professor and teacher at the UAB Microbiology Department and has a research laboratory at the UAB. He is also a full-time investigator at AHRI and lives in Durban, South Africa. He visits UAB at least six times a year.

Steyn is responsible for creating a program where students from the UAB Graduate School and School of Medicine get a unique opportunity to visit and conduct research at AHRI as part of their research training training. "Once you go to remote areas in Africa and see the destruction of the disease," said Steyn, "it only changes you. It makes a difference."

Working at AHRI provides students, especially those in medical training programs, a good opportunity to work in a sophisticated research facility located in a country with one of the world's burdened diseases. Seven UAB Ph.D. and M.D./Ph.D. students have conducted research in the Steyn laboratory in Durban as part of the annual UAB-AHRI International Summer Research Program.

Steyn Cell Report work following previous studies also using human TB lung tissue. The study, published last May in Frontiers in Immunology by Steyn and colleagues, examined the distribution of iron in sick lung TB. Iron is an important factor for growth and virulence of Mtb, but little is known about how the host controls iron availability during infection.

Steyn and colleagues found an important role for ferritin H iron storage proteins in TB control, which is directly related to HO-1. The researchers found that mouse models that had KO heavy ferritin chain genes in myeloid cells were more susceptible to TB, as indicated by an increase in the amount of Mtb in the organ, more spread of Mtb outside the lungs and a decrease in survival. In particular, a decrease in iron levels was found in pulmonary human TB.

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That Cell Report paper, "The distribution of microanatomic myeloid heme oxygenase-1 protects against free radical immunopathology in human pulmonary tuberculosis," is the result of teamwork led by first author Krishna C. Chinta. The study also included other members of the Steyn team: Vikram Saini, Joel N. Glasgow and Vineel P. Reddy at the UAB Department of Microbiology and Md. Aejazur Rahman, Kievershen Nargan and Gordon Wells at AHRI. Vikram is now at the All India Medical Science Institute, New Delhi, India.

In Alabama, collaboration with Anupam Agarwal, UAB executive vice chairman and Division director of UAB Nefrology, and James George, professor in the Division of Cardiothoracic Surgery, UAB Surgery Department, are very important for this project, said Steyn. Agarwal laboratory members Jeremie M. Lever and Amie Traylor were also involved in this study. Also, contributions by Pratistadevi K. Ramdial and Rajhmun Madansein co-authors, Albert Luthuli Inkosi Central Hospital and University of KwaZulu-Natal, Durban, South Africa, were significant.

Along with the researchers mentioned above, colleagues at Cell Report the paper is Ryan M. Wells, UAB's Department of Microbiology (currently at the University of Minnesota); Shepherd Nhamoyebonde and Alasdair Leslie, AHRI, Durban, South Africa; Gene P. Siegal, Department of Pathology UAB; and Veena B. Antony and Jessy Deshane, Division of Lungs, Allergies and Critical Care, Department of Medicine, UAB.

Support for this work comes from the National Institutes of Health grants AI111940, AI127182 and DK59600; Bill and Melinda Gates Foundation OPP1130017 award; and the South African Medical Research Council. Support also came from the UAB Center for AIDS Research and the UAB Center for Free Radical Biology.

At UAB, Agarwal holds Marie S. Ingalls, Chair of Endowed in Nephrology Leadership, George holds the Chair of Research on Cardiovascular Surgery, and Siegal holds the Robert W. Mowry Endowed Professorship in Pathology.