Exploring the associations of tobacco smoking and serum cotinine levels with selected inflammatory markers in adults with HIV in South Africa

This study examined the associations between tobacco smoking and serum cotinine levels, an objective biochemical measure of tobacco smoke exposure, with markers of inflammation, i.e., interferon-gamma (IFN-γ), interleukin 10 (IL-10), interleukin 2 (IL-2) and tumour necrosis factor-alpha (TNF-α) in people living with HIV (PLWH).These specific markers were selected because of their hypothesised associations with smoking, PLWH and their outcomes. In a random sample of ≥ 18-year-old PLWH receiving care at 17 public healthcare facilities across the Western Cape Province in South Africa, data collection included self-reported smoking history, and serum levels of cotinine and selected inflammatory markers. The inflammatory marker data were log transformed because of the skewedness of their distribution. Linear regression models (1) adjusted for age and gender, and (2) fully adjusted for age, gender, current alcohol use, body mass index and CD4 counts were used to examine the associations between smoking tobacco or serum cotinine and inflammatory markers. Level of significance was p < 0.05. Among 749 PLWH who were mainly women (79%), the mean age was 38.5 (8.9) years and similar when stratified by smoking status. Serum cotinine levels exhibited a striking discrepancy, with a median of 154 ng/mL among current smokers, in stark contrast to the consistent median values of 10 ng/mL observed among past and never smokers. In regression models adjusted for age and gender, current smoking and frequent smoking were associated with lower IL-2 but higher TNF-α. Log-cotinine exhibited associations with IFN-γ, IL-10, and TNF-α, while cotinine levels ≥ 10 ng/mL compared to < 10 ng/mL were associated with higher IFN-γ and TNF-α. In fully adjusted models, log-cotinine and cotinine levels ≥ 10 ng/mL displayed significant associations with higher IFN-γ and lower IL-2. This study underscores the importance of investigating the interplay between smoking tobacco or serum cotinine levels with pro-inflammatory cytokines in PLWH. It signals the need for comprehensive research to unravel the potential synergistic impacts of smoking tobacco and HIV infection on chronic inflammation and immune dysregulation, shedding light on critical avenues for intervention and management strategies.