Although CKD is recognized as a risk factor for the development of active tuberculosis (1,7), the literature evidence on its association with LTBI is still limited, especially based on the diverse cohort study design, the severity of the renal failure (progression stages), and diagnostic methods. To our knowledge, herein we report for the first time, the use of the fourth generation of IGRA QFT-Plus, which is designed to evaluate of Mtb-specific response by both CD4+ and CD8+ T cells, to estimate the prevalence of LTBI in different statuses of CKD and long-term hemodialysis patients in a tertiary reference center from a high TB burden area. We found that one-third of our study population had LTBI, being 32.4% in CKD and 25% in hemodialysis patients – which is higher than the estimated prevalence in the general population, where is considered that around one-fourth of the worldwide is latent infected by Mtb, as reported by WHO (2). Also, a positive CXCL-10/IP-10 assay and lack of BCG vaccination in childhood were associated to LTBI as important independent risk factors.
Considering that the screening of vulnerable populations and prophylactic treatment of LTBI are priority strategies to prevent the progression to active disease, its worth of note that patients with CKD are more susceptible to infections in general due to their compromised immune system (19). CKD progression is correlated with a reduction in CD4+ and CD8+ T cells (20), which are essential for cellular immune defense against Mtb (3). In vitro studies have demonstrated that the capacity of T cell proliferation is reduced in the uremic environment (20,21). Additionally, clinical data analysis of our cohort has revealed that 52% of participants had DM as their underlying disease, an important aspect recognized as a factor associated with both LTBI and the development of active tuberculosis (1,9). Its well-recognized that hyperglycemic condition in DM is also associated with an interfering in both innate and adaptative immune system (9). Interestingly, in our cohort, we observed LTBI in 37.9% of patients in stage 3b, followed by 31.7% in stage 4, 26.3% in stage 5, and 25% in the HD group. Based on these findings, we could speculate that, although non-statistically significant, this percentage decrease in IGRA results among the status of severity in CKD patients could be explained by a set of clinical conditions associated with the renal dysfunction and, consequently reduced capacity to build a robust or pronounced in vitro cellular immune response.
Previous studies report that high C-reactive protein (CRP) levels are attributed to the degree of pre-existing inflammation in patients with renal dysfunction (13,22,23). In our cohort, it was no different, the mean CRP levels were 6.96 mg/dL in the CKD group and 5.23 mg/dL in the HD group. From this, it is important to highlight that indeterminate results were associated with high levels of basal IFN-γ (Nil tube, data not shown), once all patients were responsive to positive control (mitogen). There were 2.7% and 8.3% indeterminate results in the CKD and HD groups, respectively. Consequently, the underlying inflammation and elevated non-specific IFN-γ levels led to indeterminate diagnostic test results.
The interaction between CKD and compromised immune response demonstrates the need for more advanced diagnostic methods to identify LTBI early. The current methods available measure the cellular memory response to the bacillus antigens, as follow: the tuberculin skin test (TST) used for more than a century (1,24) and the newest IGRA (QuantiFERON TB and T-SPOT-TB) (7,15). Studies indicate that QFT-Plus, in its 4th generation, has greater sensitivity compared to QFT-Gold In Tube (QFT-GIT), this finding can be attributed to the addition of the TB2 tube sensitized to CD8+ T cells responses (15,24). In agreement, our study observed 22.2% positive results for the TB2 tube alone, reinforcing the importance of the CD8+ T cell response in detecting latent Mtb infection.
A study conducted in Taiwan, China, using the QFT-GIT to diagnose LTBI, recorded 25% positive results among hemodialysis patients and 11% in individuals with severe CKD with eGFR < 30 mL/min/1.73 (stages 4 and 5) (25). Another study conducted in Taiwan in 2020, carried out on pre-kidney transplant individuals, observed a 20% positivity rate for the QFT-GIT (16). In Thailand, a study using the IGRA T. SPOT-TB, revealed a prevalence of 22.5% in its CKD study population, being: 25% in stage 1, 12.5% in stage 2, 25, 0% in stage 3a, 25.0% in stage 3b and 24.2% in the dialysis group (hemodialysis and peritoneal dialysis) (11). An observational-analytical study conducted in Indonesia, using the QFT-GIT, observed a positivity of 39.2% in individuals on hemodialysis (26). In Brazil, the only study conducted on this thematic, evaluated only patient on hemodialysis and identified a prevalence of LTBI in 8.5% of patients, using the tuberculin skin test as a LTBI diagnostic method (27). It is important to highlight that, Taiwan, Thailand, Indonesia, and Brazil are among the 30 countries with the highest incidence of TB in the world (2).
Using multivariate logistic regression analysis (28,29), it was possible to demonstrate the independent risk factors associated with QFT-Plus positivity in our study population. Our results revealed that the lack of BCG vaccination in childhood (adjusted OR: 7.41 [95% CI: 2.15-25.48]; p = 0.0014) was an independent risk factor for a positive result in the diagnostic test. In a meta-analysis evaluating BCG-vaccinated and unvaccinated children who were exposed to tuberculosis, using QFT-GIT test, it was shown that BCG protects against Mtb infection and prevents progression to active disease (28,29). A systematic review demonstrated that BCG vaccination offers protection against pulmonary and extrapulmonary tuberculosis for up to 10 years. However, most of these studies did not follow participants long enough or had a low number of cases after 15 years. These results should not be interpreted as indicating no effect (30). In agreement with our work, a study that investigated the incidence of LTBI in pre-transplant kidney patients found that non-vaccination with BCG was strongly associated as an independent risk factor for the development of LTBI (24).
We also found that the positivity in the CXCL-10/IP-10 assay was also considered an independent risk factor for the diagnosis of LTBI (aOR: 4.48 [1.87-10.76]; p = < 0.001). Based on our data, we can observe that high levels of CXCL-10/IP-10 in CKD and HD patients were associated with a significant increase in the probability of developing LTBI, estimated at 4.48 times. IFN-γ-inducible protein 10 (IP-10), a member of CXC chemokine family (XCXC-10), acts recruiting immune cells to the site of infection. This process occurs in synergy with IFN-γ, in response to the recognition of Mtb-specific antigens by specific T cells (31–33). In a recent study, increased levels of IFN-γ and CXCL-10/IP-10 were highlighted in patients with active TB compared to healthy individuals (33). While IFN-γ is produced mainly by T lymphocytes, CXCL-10/IP-10 is produced by numerous cells including the innate immune system such as monocytes and antigen-presenting cells (APCs) (31,33,34). These data point out this chemokine as a potential adjuvant biomarker, in association with IFN-γ for the detection and monitoring of LTBI, which might improve diagnostic accuracy and early intervention. A recent study from our research group reported that individuals with pulmonary TB who had both positive IFN-γ and CXCL-10/IP-10 had increased CD64 expression compared to individuals with LTBI (18).
As limitations of this study, we could point out: i) a comparison between QFT-Plus and TST was not analyzed due to instability in the distribution of the test in Brazil in the period of participant recruitment; ii) relatively small number of individuals in the study population due to the criteria of eligibility and infrastructure capacity by the hospital, especially for HD group; iii) because the study was conducted in a reference center and tertiary health unit of health (high complexity), we could not exclude this bias; iv) we did not carried out comparisons with health control group. Despite these observations, our study can be considered a pioneer in Brazil when using the QFT-Plus test to evaluate LTBI infection in this cohort population, which could be well characterized by clinical and laboratory aspects and followed for a long period at HUPE/UERJ.
In conclusion, approximately 32% of patients with CKD and 25% of those undergoing HD were diagnosed with LTBI. Our study population demonstrated a positivity rate of 39.1% in the CXCL-10/IP-10 assay, with rates of 40.5% in the CKD group and 33.3% in the HD group, highlighting its potential as a relevant biomarker for LTBI in CKD patients. The absence of BCG vaccination during childhood and elevated levels of the CXCL-10/IP-10 biomarker were identified as higher risk factors for LTBI. Furthermore, our data show that QFT-Plus is a useful tool in LTBI detection among CKD patients in late and terminal stages. Finally, these findings reinforce and base to the need of preventive strategies and continuous surveillance for LTBI, emphasizing the relevance of innovative diagnostic approaches which may contribute to a significant TB control in high-risk populations.