Transforming growth factor-beta decreases survival of Mycobacterium bovis-activated T cells.
BACKGROUND
A comprehensive understanding of the immune response induced by Mycobacterium bovis Bacille Calmette-Guérin in activation of protective T cells against tuberculosis is important to develop effective therapies to combat this disease. In this study, our experiments were designed to determine effects of transforming growth factor (TGF)-beta on M. bovis-induced T-cell activation and survival.


METHODS
Fluorescence-activated cell sorter (FACS) analysis was used for detection of apo-ptotic cells by three different methods: 1). scattered light change during early phase of apoptosis; 2). detection of hypodiploid DNA, or 3). terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) technique. Quantification of positively stained population was based on samples stained with isotype control antibodies analyzed on a FACScan.


RESULTS
TGF-beta added at initiation of culture did not alter percentage of viable cells. By contrast, TGF-beta added 72 h post-activation decreased percentage of viable cells. This effect was statistically significant (p <0.05). Furthermore, addition of anti-TGF-beta MoAb together with TGF-beta abolished the ability of this cytokine to decrease survival in post-activated human T cells. Role of TGF-beta on post-activated human T cells was further confirmed by staining apoptotic nuclei with propidium iodide, which detects late events of apoptosis, and by DNA fragmentation determined using TUNEL assay. Interestingly, TGF-beta did not promote Fas-mediated killing. Finally, TGF-beta increased apoptosis of CD4(+) T cells after mycobacterial stimulation.


CONCLUSIONS
This study indicated an important role for TGF-beta in suppression of protective immune response against M. bovis by promoting elimination of post-activated T cells. Furthermore, results showed that TGF-beta had no direct effect on M. bovis-induced up-regulation of Fas (CD95).
Hernández-Garay
Marisol
M
Departamento de Inmunología, Escuela Nacional de Ciencias Biológicas, ENCB, Instituto Politécnico Nacional, IPN, Mexico City, Mexico.
Méndez-Samperio
Patricia
P
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002417:Cattle; D002469:Cell Separation; D002470:Cell Survival; D005434:Flow Cytometry; D006801:Humans; D008213:Lymphocyte Activation; D009163:Mycobacterium bovis / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D019014:fas Receptor / Q000378:metabolism
D016212:Transforming Growth Factor beta; D019014:fas Receptor