Correlation of the Precursor Frequency of CD4 + Effector Memory T Cells With Induration Measured in the Tuberculin Skin Test (TST)
Tuberculosis (TB) is a major global health concern. One third of the world's population is
infected with Mycobacterium tuberculosis. Two to 3 million people die every year of the
disease with 8-10 million new cases per year. It is projected that there will be 90 million
new cases and 30 million deaths over the next decade. For a disease, which we know to have
existed since 2400 BC, our understanding of its pathogenesis is incomplete, especially in
relation to the human immune response and the role of lymphocytes in particular.
The purpose of the present study is to evaluate the latent form of this infection, the
prevalence of which worldwide exceeds that of active disease. Our hypothesis is that in
latent tuberculosis antigen specific effector memory CD4+ T cells are responsible for the
generation of clinically measurable delayed type hypersensitivity and that central memory
CD4+T cells are not directly involved in this process. We base this idea on the assumption
that latent tuberculosis is a state of antigen persistence and that effector memory T cells
should be maintained as long as antigen/infection is present.
We propose to conduct this study in Mali, West Africa and local clinics in the U.S.
Tuberculosis affects 593/100,000(2) individuals in Mali and most have been exposed to the
disease. Additionally it would be important to evaluate the same parameters locally as
latent infection is one of the major factors for reactivation tuberculosis in this country.
Patients would be enrolled in 4 major groups: HIV-/TST- (Group A), HIV-/TST+ (Group B),
HIV+/TST+ (Group C) and HIV+/TST- (Group D).
To evaluate this hypothesis we plan to enroll between 100 - 300 patients over the course of
2 years from both countries. Blood samples before and at predetermined time points after
the application of Purified Protein Derivative (PPD) will be obtained to determine the
fraction of CD4+ T cells which produce interferon gamma in response to stimulation with PPD
with a 16hr antigen stimulation assay. Appropriate staining will be done to ascertain the
phenotype as well as cytokine production (Interferon gamma, ( IFN gamma), Interleukin 2
(IL2) and Tumour Necrosis Factor (TNF)). Additionally lymphocyte proliferation will be
studied using 5-(and-6)-carboxyflouorescein diacetate succinimidyl ester (CFSE.)
In conducting this study we hope to further the understanding of the immune mechanisms
involved, particularly mechanisms of T cell memory, which would provide insights into TB and
HIV pathogenesis. We also believe that understanding these mechanisms could lead towards
establishment of surrogates for immunity in TB vaccine studies, which could enhance vaccine
trial design. It might also help in understanding better the immunological dynamics of
tuberculosis co-infection in individuals with HIV infection.
Sophia B Siddiqui, M.D.
National Institute of Allergy and Infectious Diseases (NIAID)
United States: Federal Government
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