Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis infection, primarily affecting the lungs (WHO, 2024). According to the Global Tuberculosis Report 2024 of the World Health Organization (WHO), approximately 10.8 million people worldwide developed TB in 2023, with about 1.25 million deaths, including 1.09 million HIV-negative individuals and 161000 people living with HIV/AIDS (PLWHA) (Schito et al., 2015; WHO, 2024). TB remains among the leading causes of infectious disease mortality globally, imposing a substantial disease burden (Schito et al., 2015; GBD 2019 Diseases and Injuries Collaborators, 2020). Within individual hosts, HIV/TB co-infection creates a bidirectional pathogenic synergy, accelerating immune deterioration and disease progression (Bruchfeld et al., 2015; Liebenberg et al., 2021). Following infection with Mycobacterium tuberculosis, the majority of individuals remain in a state of latent tuberculosis infection (LTBI), characterized by persistent immune responses to mycobacterial antigens without clinical manifestations of active TB. Approximately 5%-10% of LTBI cases in the general population progress to active TB (Jiang et al., 2022), whereas for PLWHA, the risk of LTBI progressing to active TB is 20–37 times higher than in HIV-negative individuals (Jiang et al., 2022).

CD4⁺ T lymphocytes are the primary target cells of HIV infection. HIV infection leads to progressive depletion of CD4⁺ T lymphocytes (Vidya Vijayan et al., 2017). Through effective antiretroviral therapy (ART), CD4⁺ cell count can gradually recover to near-normal levels (Xiao et al., 2022). However, despite effective viral suppression and CD4⁺ cell count recovery, immune activation often persists, and CD8⁺ cell levels remain difficult to normalize after ART (Helleberg et al., 2015). Therefore, relying solely on CD4⁺ cell count does not fully reflect the immune function recovery status of PLWHA.

The CD4/CD8 ratio is an important indicator for predicting immune dysfunction and disease progression in PLWHA. HIV infection typically causes CD4/CD8 ratio inversion, and while ART may restore the CD4/CD8 ratio, it rarely exceeds 1, especially in patients with delayed treatment initiation (Serrano-Villar et al., 2014). Even when CD4⁺ cell count exceed 500 cells/μL and viral load falls below the detection limit in PLWHA, CD4/CD8 ratio inversion persists for extended periods (Xiao et al., 2025). Compared with CD4⁺ cell count alone, the CD4/CD8 ratio is a more accurate indicator for evaluating immune status during ART.

This study employed QuantiFERON-TB Gold In-Tube (QFT) to detect LTBI among PLWHA in regions with low prevalence of TB, and explored factors associated with LTBI in the PLWHA. PLWHA with active TB, previous TB history, or indeterminate QFT results were excluded based on clinical manifestations, comprehensive physical examinations, imaging, and etiological test results.

Through this cross-sectional study conducted among PLWHA, we found that PLWHA aged 45-<60 years had significantly higher LTBI risk compared to those <45 years old. Notably, the dose-response relationship between CD4⁺ cell count and LTBI risk showed an increasing trend, while the dose-response relationship between CD8⁺ cell count and LTBI risk demonstrated a decreasing trend. Furthermore, a significant non-linear dose-response relationship was observed between CD4/CD8 ratio and LTBI risk, with LTBI risk in PLWHA showing an upward trend as the CD4/CD8 ratio increased.

Among the 1184 PLWHA included in this study, the LTBI rate detected by QFT was 8.4%, which was lower than the LTBI rates of PLWHA reported in Ningxia (24.4%) (Jiang et al., 2022), Changzhou (10.02%) (Zhang et al., 2020), and Xian (8.8%) (Xin et al., 2017) in China. Jiangsu Province is a low TB prevalence area (Xiong et al., 2024), which may be one of the reasons for the relatively low LTBI rate among PLWHA in this survey.

Multivariable analysis showed that, compared with PLWHA aged <45 years, those aged 45 to <60 years had higher risk of LTBI (OR = 2.158; 95% CI: 1.339-3.478; P = 0.002). This corresponds to approximately a two-fold increase in the odds of LTBI among PLWHA aged 45-<60 years. The 95% confidence interval is relatively narrow, indicating reasonable precision of the estimate. This finding is consistent with related research findings (Mancuso et al., 2016).In China, the first national TB epidemiological survey, conducted in 1979, reported an active pulmonary TB prevalence of 717 per 100,000, indicating widespread community transmission at that time. Subsequent national surveys in 1984/1985, 1990, 2000, and 2010 showed only gradual declines in TB prevalence (Tu, 2013). Taken together, these findings suggest that TB prevalence and community transmission in the 1960s and 1970s were higher than in later decades, and that adults currently aged 45 to 60 years, most of whom were born in the 1960s and 1970s, may therefore have faced a higher risk of TB exposure earlier in life and accumulated latent infection risk. Meanwhile, the body experiences accumulated TB exposure risk with age and age-related subtle changes in the immune system [such as immunosenescence (Fulop et al., 2018) or inflammaging (Li et al., 2023)]. Research has shown that increasing age is a major risk factor for developing and dying from TB, as aging is accompanied by declining immune system function, making elderly individuals more susceptible to TB infection (Li et al., 2019). Furthermore, middle-aged PLWHA show significantly slower CD4⁺ T cell recovery after antiretroviral therapy compared to younger PLWHA (Manfredi, 2002), suggesting that even with antiretroviral treatment, their immune reconstitution remains relatively insufficient, potentially making latent TB difficult for the body to clear or control.

Studies have found that the CD4/CD8 ratio is increasingly recognized as a more sensitive and comprehensive indicator of immune health than CD4⁺ cell count (Luo et al., 2024) and can serve as a biomarker for non-AIDS-related diseases (Mussini et al., 2015). In the present study, we observed that multivariate analysis showed that PLWHA with CD4/CD8 ratio ≥1 had markedly higher odds of LTBI than those with CD4/CD8 ratio <0.3 (OR = 3.562; 95% CI: 1.627-7.800), indicating more than a three-fold increase in odds. However, the 95% confidence interval is relatively wide, suggesting considerable uncertainty around the magnitude of the association. Therefore, this estimate should be interpreted cautiously and verified in larger studies. This finding is consistent with previous studies’ finding that immune recovery is independently associated with QFT positivity rate (Danel et al., 2014; Mthembu et al., 2023). The mechanism may be related to enhanced CD4⁺ T cell-mediated immune responses. The core principle of IGRAs is to detect the ability of T cells to produce IFN-γ after stimulation with Mycobacterium tuberculosis-specific antigens (Chinese Society for Tuberculosis, Chinese Medical Association, 2022). When the CD4/CD8 ratio ≥1, CD4⁺ T cell-dominated Th1-type immune responses can promote interferon-gamma release after stimulation with TB-specific antigens (ESAT-6/CFP-10) (Prezzemolo et al., 2014), thereby improving QFT detection sensitivity. Conversely, a CD4/CD8 ratio <1 suggests that excessive activation of CD8⁺ T lymphocytes may lead to immune exhaustion, suppress antigen-specific responses, and increase false-negative risk (Serrano-Villar et al., 2014). A CD4/CD8 ratio ≥1 in this study may more likely indicate a detectable IFN-γ sensitization state rather than increased LTBI incidence risk. A study by Lu P et al. indirectly supports this view (Lu et al., 2025), demonstrating that QFT detection sensitivity remains relatively stable in PLWHA with relatively high CD4⁺ cell count. This suggests that a higher CD4/CD8 ratio may reflect sufficient immune response capacity to support accurate QFT detection results. A low CD4/CD8 ratio in PLWHA may signal higher true TB risk (Liu et al., 2023), but it can also impair test sensitivity, meaning both clinicians and researchers must carefully factor immune status into LTBI screening. Considering epidemiologic risk and immune function is needed to avoid mistaking immune-related test variations for differences in actual TB infection. This study further analyzed differences in QFT detection results at different CD4/CD8 ratio levels and found no statistically significant difference in QFT positivity rates between PLWHA with CD4/CD8 ratio <0.3 and those with 0.3≤CD4/CD8 ratio <1. This result suggests that in immune imbalance states where the CD4/CD8 ratio is below 1, the body’s immune response to TB antigens is uniformly significantly limited, with consistently elevated false-negative risk in IGRA detection. Therefore, individuals with CD4/CD8 ratio <0.3 and 0.3≤CD4/CD8 ratio <1 can be considered to have the same immune imbalance level. CD4/CD8 ratio ≥1 may be the optimal threshold for screening LTBI risk in PLWHA, while immune imbalance below this value may lead to increased false-negative risk in QFT detection.

To further explore the relationship between CD4/CD8 ratio and LTBI risk in PLWHA, we used a restricted cubic spline (RCS) model to fit the dose-response relationship between CD4⁺ cell count, CD8⁺ cell count, CD4/CD8 ratio, and LTBI risk. The results showed a non-linear relationship between CD4⁺ cell count and LTBI risk. As CD4⁺ cell count increases, the LTBI risk in PLWHA increases, peaking when CD4⁺ cell count reaches 793 cells/μL, and then the risk decreases. Jiang et al. (2022) demonstrated that within a certain range, when CD4⁺ cell count is lower, the risk of LTBI in PLWHA gradually increases as CD4⁺ cell count rises, which is consistent with the trend observed in this study. Additionally, compared with PLWHA whose CD4⁺ cell count <800cells/μL, LTBI risk begins to decrease after the CD4⁺ cell count reaches 800 cells/μL in PLWHA, which is similar to the finding in this study (Jiang et al., 2022). This may be because PLWHA have impaired immune function, with suppressed cellular immunity and hypersensitivity reactions, leading to a weak or even absent QFT response and thus a lower LTBI risk. As the CD4⁺ cell count increases, the sensitivity of QFT diagnosis also improves (Song, 2025). As CD4⁺ cell count recover with ART, the risk of tuberculosis infection gradually decreases, and QFT positive rates decline, indicating a reduced risk of LTBI (Suthar et al., 2012).

The CD4/CD8 ratio in PLWHA showed a significant non-linear dose-response relationship with LTBI risk. As the CD4/CD8 ratio increases, the risk of LTBI increases. Wong et al. (2019) found that increased LTBI incidence correlates with higher CD4/CD8 ratios, consistent with our findings. The reason for this is similar to the previous explanation: due to immune impairment in PLWHA, cellular immunity and hypersensitivity reactions are suppressed, leading to a weak or absent QFT response and lower positivity rates, as confirmed by Yu et al. (2022). In the RCS model, participants with CD4/CD8 ratios < 1 showed lower odds of QFT positivity compared with those with higher ratios. In the context of PLWHA, CD4/CD8 ratio < 1 generally reflects incomplete immune reconstitution and more pronounced immune dysfunction, which can reduce the sensitivity of the QFT assay and increase the likelihood of false-negative results (Castilho et al., 2022). Thus, the lower odds of QFT positivity in individuals with CD4/CD8 < 1 likely reflect reduced ability to mount a detectable IFN-γ response, rather than a lower underlying risk of LTBI. as the CD4/CD8 ratio increases, immune recovery progresses, enhancing diagnostic sensitivity (Yu et al., 2022). The RCS model showed that when the CD4/CD8 ratio ≥1, the increase in LTBI risk gradually slows down, reinforcing the idea that CD4/CD8 ≥1 could be the threshold for LTBI screening in PLWHA. In the RCS results, the confidence intervals around the spline curves were relatively wide at the lower and higher ends of CD4, CD8, and CD4/CD8. The smaller number of participants in these extreme ranges results in reduced precision of the estimates. Consequently, the apparent non-linear trends at the tails of the curves should be viewed as exploratory, and future studies with larger sample sizes in these ranges are needed to confirm these findings.

This study has several limitations. First, the cross-sectional design only provides a snapshot of CD4⁺ and CD8⁺ cell counts, viral load, and QFT results at one point in time. Therefore, it is not possible to determine temporal relationships or draw causal inferences between immune status, viral replication, and QFT positivity. Additionally, the Chinese Center for Disease Control and Prevention reports that the male-to-female ratio among newly reported HIV infection cases in 2024 was 3.2:1 (approximately 23.8% female) (National Center for AIDS/STD Control and Prevention, Chinese Center for Disease Control and Prevention, 2025). However, in our study, the proportion of females recruited was only 9.9%, which is not representative of the general population. This gender imbalance limits the statistical power for sex-stratified analyses and may reduce the generalizability of our findings to females.

In conclusion, this cross-sectional study explored factors associated with QFT-defined LTBI risk in PLWHA and applied a restricted cubic spline model to characterize potential non-linear relationships. We observed that PLWHA aged 45-<60 years appeared to have a relatively higher risk of QFT-defined LTBI, and that a CD4/CD8 ratio≥1 might represent a more favorable range for identifying LTBI risk in this population. If confirmed in future prospective studies, these findings may support a more targeted approach when performing LTBI screening using QFT in PLWHA, with particular attention to middle-aged PLWHA (45-<60 years) and consideration of stratified screening strategies: (1) In PLWHA with a CD4/CD8 ratio ≥1, QFT detection alone can be used; (2) In those with a CD4/CD8 ratio <1, it may be prudent to combine QFT with other TB-specific tests and to monitor changes in the CD4/CD8 ratio over time. Given the cross-sectional design and the use of QFT positivity as an operational definition of LTBI, these recommendations should be viewed as exploratory, and future studies incorporating multidimensional immune markers and clinical outcomes are needed to further validate their application value.