Document Type


Date of Original Version



Cell & Molecular Biology


Introduction: Spontaneous interferon‐γ (IFNγ) released detected by enzyme‐linked immunospot (ELISpot) assays may be a biological phenomenon. Markers of immune activation levels were assessed as correlates of high background among individuals in Kenya. Methods: Couples concordantly seronegative for HIV‐1 were enrolled. IFN‐γ ELISpot assays were conducted and negative control wells were categorized as having either high or low background (≥50 and <50 SFU/106 peripheral blood mononuclear cells [PBMC], respectively). PBMC were stained for CD4, CD8, and immune activation markers (CD38 and HLA‐DR) and analyzed using flow cytometry. Proportions of activated T‐cells were compared between those with low and high background by Mann–Whitney U test. Correlates of background SFU and immune activation were assessed using regression models. Results: Among 58 individuals, 14 (24%) had high background. Frequencies of CD4+CD38+HLA‐DR+ and CD8+CD38+HLA‐DR+ cells were higher in individuals with high background compared to those with low background (P = 0.02). Higher background SFU was associated with history of sexually transmitted infections (P = 0.03), and illness in the past 3 months (P = 0.005), in addition to increased levels of activated CD4+ and CD8+ cells (P range = 0.008–0.03). Female gender and male circumcision decreased levels of CD4+ and CD8+ immune activation (P range = 0.002–0.03). Additionally, higher background SFU and activated CD4+ and CD8+ cells were individually associated with positive ELISpot responses to HIV‐1 peptide pools (P range = 0.01–0.03). Conclusions: These findings suggest that increased basal immune responses may be a biological mechanism contributing to higher background ELISpot SFU. Systematic exclusion of data from individuals with increased background in IFN‐γ release assays may bias results in population‐based studies.

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