XML Feed for RxPG News   Add RxPG News Headlines to My Yahoo!   Javascript Syndication for RxPG News

Research Health World General
 
  Home
 
 Latest Research
 Cancer
 Psychiatry
 Genetics
 Surgery
 Aging
 Ophthalmology
 Gynaecology
 Neurosciences
 Pharmacology
 Cardiology
 Obstetrics
 Infectious Diseases
  AIDS
  Influenza
  MRSA
  Tuberculosis
  Shigella
  HCV
  SARS
  Ebola
  Dengue
  Malaria
  Pertussis
  Mumps
  Prion Diseases
  Small Pox
  Anthrax
  Leishmaniasis
 Respiratory Medicine
 Pathology
 Endocrinology
 Immunology
 Nephrology
 Gastroenterology
 Biotechnology
 Radiology
 Dermatology
 Microbiology
 Haematology
 Dental
 ENT
 Environment
 Embryology
 Orthopedics
 Metabolism
 Anaethesia
 Paediatrics
 Public Health
 Urology
 Musculoskeletal
 Clinical Trials
 Physiology
 Biochemistry
 Cytology
 Traumatology
 Rheumatology
 
 Medical News
 Health
 Opinion
 Healthcare
 Professionals
 Launch
 Awards & Prizes
 
 Careers
 Medical
 Nursing
 Dental
 
 Special Topics
 Euthanasia
 Ethics
 Evolution
 Odd Medical News
 Feature
 
 World News
 Tsunami
 Epidemics
 Climate
 Business
 
 India
Search

Last Updated: Nov 18, 2006 - 12:32:53 PM

Tuberculosis Channel
subscribe to Tuberculosis newsletter

Latest Research : Infectious Diseases : Tuberculosis

   DISCUSS   |   EMAIL   |   PRINT
Explaining Why People of African Descent Are More Vulnerable to TB
Feb 25, 2006 - 10:06:00 AM, Reviewed by: Dr. Priya Saxena

�Our results indicate that we have much yet to learn about human immune responses to infections. They also emphasize the importance of vitamin D in human immune responses, and suggest that it is now important to learn how much vitamin D is optimal for innate immunity, and how that can best be achieved through diet or supplementation,�

 
A team of scientists has identified a cellular mechanism that may help explain the puzzle of why people of African descent are more susceptible to tuberculosis infection and why, once infected, they develop more severe states of the disease than whites. The team includes researchers from University of California, Los Angeles (UCLA), and Harvard School of Public Health (HSPH).

Approximately eight million people worldwide are infected with TB annually, with an estimated two million people dying from the lung disease each year. TB is caused by the pathogen Mycobacterium tuberculosis, but infection does not automatically result in full-blown disease. In the U.S., minority and foreign-born populations have significantly higher rates of TB than the overall U.S. average, according to the Centers for Disease Control and Prevention. In 2004, African Americans had TB case rates that were eight times higher than whites.

Scientists have understood that mice -- a frequently used animal model in experiments -- combat microbes such as TB by producing nitric oxide in scavenger cells of the immune system known as macrophages. However, this mechanism is not prominent in humans, and the mechanism by which human macrophages kill the tubercle bacillus has remained an additional puzzle. Innate immunity is the rapid immune response of host scavenger cells to recognition of certain patterns of molecules found on pathogens, which has been retained in evolution from fruit flies to humans. A set of receptors on macrophages in humans called Toll-like receptors contribute to innate immune responses. The researchers describe a novel pathway used by human macrophages that may be critical to resisting infection with certain pathogens and that turns out to be critically dependent on vitamin D. This description provides a different way to think about how human immune systems battle pathogens in general.

The research team found that when Toll-like receptors in humans are stimulated by specific molecules of the tubercle bacillus, vitamin D receptors and an enzyme called Cyp27B1, which converts the vitamin from an inactive form to an active form, are dramatically increased. The result of this dual activation is the cleavage of a preexistent protein to a small peptide called cathelicidin, which can kill TB bacilli in the test tube. One of the interesting aspects of this mechanism is that production of vitamin D in humans is dependent on exposure to UV light, generally sunlight, and may not have evolved in mice since they are nocturnal animals.

"These studies began with a very basic exploration of differences in gene expression in two related human white blood cell types known to be involved in host responses to infection, and concluded by revealing a new and potentially important human mechanism for killing intracellular pathogens,� said Philip Liu, postdoctoral scholar in the Department of Immunology and Molecular Genetics at the David Geffen School of Medicine at UCLA and co-lead author of the paper.

African Americans have significantly lower levels of vitamin D in their blood serum than whites because higher levels of melanin -- the pigment that provides color to skin absorbs UV light and reduces African Americans' ability to produce vitamin D. When the macrophages were stimulated by molecules of the tubercle bacillus that trigger Toll-like receptors, the research team found that cells cultured in serum provided by African Americans produced 63 percent less of the microbe-killing cathelicin than when cultured in serum from whites. Supplementing the serum from African Americans with vitamin D precursor to a range found in serum samples from whites boosted the induction of cathelicidin.

Scientists have long known that African Americans have less vitamin D than whites and that they are more vulnerable to TB. This study helps to resolve two of the puzzles of tuberculosis, the differences between mice and human antibacterial mechanisms, and the susceptibility of people of African and possibly Asian descent to tuberculosis. The researchers suggest a need for clinical trials to investigate the effect of vitamin D supplementation.

�Our results indicate that we have much yet to learn about human immune responses to infections. They also emphasize the importance of vitamin D in human immune responses, and suggest that it is now important to learn how much vitamin D is optimal for innate immunity, and how that can best be achieved through diet or supplementation,� said the senior investigator of these studies, Dr. Robert Modlin, Klein Professor of Dermatology and Professor of Microbiology, Immunology and Molecular Genetics at the David Geffen School of Medicine at UCLA.

�Tuberculosis is a devastating disease that strikes vulnerable populations particularly hard," said immunologist Barry R. Bloom, Dean of the Faculty at HSPH and a co-author of the paper. "This study provides a new mechanism for innate immunity in humans and demonstrates how variations in vitamin D synthesis may make individuals susceptible to TB infection. It is exciting to consider the possibility that innate immunity to tuberculosis and other infections in vulnerable populations might be enhanced by providing a simple vitamin that would cost only pennies a day.�
 

- The paper will appear online in the February 23 issue of Science Express.
 

www.hsph.harvard.edu

 
Subscribe to Tuberculosis Newsletter
E-mail Address:

 

This research was supported by grants from the National Institutes of Health and the German Research Foundation.

Harvard School of Public Health is dedicated to advancing the public's health through learning, discovery, and communication. More than 300 faculty members are engaged in teaching and training the 900-plus student body in a broad spectrum of disciplines crucial to the health and well being of individuals and populations around the world. Programs and projects range from the molecular biology of AIDS vaccines to the epidemiology of cancer; from risk analysis to violence prevention; from maternal and children's health to quality of care measurement; from health care management to international health and human rights.


Related Tuberculosis News

Emergence of highly drug-resistant tuberculosis strains requires urgent action
Treating populations infected with HIV and latent TB could speed the emergence of drug-resistant TB
Solution to TB epidemic may lie in protective Heme oxygenase 1 protein
Explaining Why People of African Descent Are More Vulnerable to TB
Indian Scientists Identify Key Genes in Tuberculosis Infection
PA-824 holds promise for shortening the TB treatment regimen
DC-SIGN expressing alveolar macrophages are preferentially targeted by M. tuberculosis
Tuberculosis Still a Risk for Patients on Anti-retrovirals
Evolutionary history of tuberculosis is shaped by human migration patterns
TB vaccines will fail in developing countries


For any corrections of factual information, to contact the editors or to send any medical news or health news press releases, use feedback form

Top of Page

 

© Copyright 2004 onwards by RxPG Medical Solutions Private Limited
Contact Us