Decreased expression of perforin in CD8(+) T lymphocytes in patients with Mycobacterium tuberculosis infection and its potential value as a marker for efficacy of treatment.

BACKGROUND: Cytolytic activity against mycobacteria tuberculosis (MTB) within the infected macrophage is a crucial step in the immunity against TB infection, as MTB is an intracellular bacterium. Cytotoxic molecules such as perforin and granzymes produced by cytolytic T cells directly participate in this process. In this study, we evaluated the cytotoxicity function employing flow cytometry analysis of the level of expression of interferon-γ (IFN-γ), perforin and granzyme B in CD8(+) T cells from patients with active pulmonary TB (PTB), stable PTB and healthy controls, and explored whether MTB antigen (MTB Ag)-stimulated cytotoxic molecules would be useful for monitoring responses to anti-TB treatment.

METHODS: Intracellular IFN-γ, perforin, and granzyme B were measured by flow cytometry in CD8+ T lymphocyte populations from peripheral blood mononuclear cells before and after stimulation with ESAT-6 and CFP-10 peptides for 72 hours. A total of 38 healthy controls, 52 PTB patients after treatment for 2 months and 58 patients with active PTB were enrolled.

RESULTS: The positive rate of IFN-γ+ CD8(+) T cells was expressed higher in active PTB patients and stable PTB compared to healthy controls. Expression of perforin in CD8(+) T lymphocytes was lower in the active PTB than the stable PTB. Positive downregulation of perforin and granzyme B after stimulation with ESAT-6 and CFP-10 peptides in active PTB and stable PTB was seen. IFN-γ was upregulated after stimulation. ROC curve analysis showed that the area under the curve (AUC) of perforin and perforin + IFN-γ after stimulation were 0.766 (P=0.000), 0.802 (P=0.000), respectively.

CONCLUSIONS: Our results show that expression of perforin in CD8(+) T lymphocytes is downregulated in PTB infection and ESAT-6 and CFP-10 peptides might participate in the downregulation process. This finding cautiously suggests that MTB Ag-stimulated perforin downregulation and IFN-γ upregulation might be a potential index for monitoring therapy response in active PTB patients.