Peripheral Blood CD8 T Cell Response in Different Phases of MTB Infection

Abstract

A reliable approach differentiating between active and latent TB infection (LTBI) is yet unavailable. Recent data suggest the involvement of CD8 T cells in protective response to mycobacterium tuberculosis (MTB). We compared the antigen-specific responses and subset composition of peripheral blood CD8 T cells in patients with active infection (ATB), recent household contacts (RC), highly-exposed health-care workers (HW), and BCG-vaccinated healthy controls (HC). Study groups included 20 ATB, 21 RH, 21 HW and 15 HC. Active TB was diagnosed according to microbiological and clinical criteria. RD1-specific CD4 and CD8 T cells were determined by intracellular cytokine staining (ICS). CD8 T subsets were defined as naïve (CD45RA+CD27+), memory (M, CD45RA-CD27+), effector (E, CD27-CD45RA-), and terminal effector (TE, CD27-CD45RA+), and analyzed by flow cytometry. The levels of RD-1-specific CD4 T cells were highest in ATB but not significantly different from LTBI groups. A significant RD-1-specific CD8 T cell IFNγ response (0.289%) differentiated RC from ATB, HE and HC subjects (0.053, 0.027 and 0.011, p < 0.05) and was associated with decreased M/TE ratio. Finally, an increased M/E CD8 T ratio distinguished HW from RC and ATB subjects (7.6 vs. 2.4 and 2.6, p < 0.05). The study of MTB-specific CD8 T-cell response in combination with CD8 T subset composition adds to the differentiation between active and latent TB.Key words: CD8 T-cell response, RD-1-specific T cells, ICS, MTB infection 587 Introduction. Mycobacterium tuberculosis (MTB) is one of the most frequent causes of infectious morbidity worldwide [ 1 ]. A large majority of M. tuberculosis-infected individuals remains asymptomatic while unable to clear the bacterium, with a lifelong probability to develop active TB of about 5-10% [ 2 ]. This probability is highest within the first two years after infection, and in subjects with recently-established LTBI preventive therapy can be effective. Thus the distinction between the different forms and stages of MTB infection is fundamental for the effective control of TB transmission.The correct diagnosis of LTBI remains a challenge. Until recently, tuberculin skin test (TST) has been the most frequently used screening method, leading to a high rate of false positive results in M. bovis BCG-vaccinated individuals, and false negative tests in immunosuppressed persons. The new interferon gamma release assays (IGRAs) employing RD-1 antigens specific for virulent mycobacteria have excellent specificity unaffected by BCG vaccination and increased sensitivity While CD4 Th1 cells are the well-known effectors of MTB-specific immune response, a lot of evidence from humans and from animal models indicate a critical role of CD8 T cells for MTB control as well [ 6-8 ]. However, data about the characteristics of CD8 T cell responses in individuals with LTBI and in patients with active tuberculosis are still scarce.In this study, using intracellular cytokine staining (ICS) and flow cytometry, we compared the CD8 T cell responses ...

T Cell Effector and Regulatory Subsets, Differentiating Between Active and Latent MTB Infection

“…We have previously described accumulation of CD45RA-CD27+ CD8 T cells in stable LTBI as compared to ATB [26]. Our present results are not contradictory, since the CD45RA-CD27+ subset is contained within the CD45RA/ CCR7-defined EM population.…”