Elderly individuals exhibit dysregulated monocyte responses to viral immune complexes compared to adults and children

Abstract

The severity of certain viral infectious diseases varies across the age; we hypothesize that these variations could be related to the variation of immune responses to viral immune complexes (ICs) among the age. This study aimed to investigate monocyte activation in response to ICs in children, adults, and elderly individuals. An experimental in vitro model was established using peripheral blood mononuclear cells from healthy individuals. Monocyte activation markers (CD169, CD38, HLA-DR), the negative co-stimulatory molecule (PD-L1), and cytokine production were measured under basal conditions and upon stimulation with human adenovirus 5-IgG immune complex (Ad5-ICs), interferon-alpha (IFN-α), and lipopolysaccharide (LPS). Monocytes from children and adults displayed similar activation profiles in response to ICs and IFN-α stimulation, characterized by increased expression of CD169 and PD-L1. In contrast, monocytes from elderly individuals exhibited weak or no overexpression of CD169 and PD-L1 coupled with a diminished PBMC cytokine response. Notably, cells from elderly participants produced high levels of TNF-α, IL-1α, and IL-6 in the absence of stimulation. Multiple comparisons confirmed reduced monocyte activation and PBMC cytokine responses in the elderly compared to adults and children. Although children exhibited a significant response to ICs, their secretion of IFN-α, IP-10, IFN-γ, IL-8, and IL-2 was lower than that observed in adults. Our findings suggest that elderly individuals have poor and dysregulated responses to ICs, likely due to immunosenescence and chronic inflammation. Adults exhibit a robust and balanced response to ICs, while children display a moderate response, possibly influenced by 'trained immunity' resulting from frequent early-life exposures to pathogens. These insights highlight the importance of further research to develop age-specific therapeutic strategies to modulate immune function during viral IC exposure.

Keywords: Immune complexes; Immunosenescence; Inflammaging; Monocytes activation.

Fig. 1

A. Overview of Experimental Protocol. B. Gatting strategy: PBMCs were first gated based on FSC/SSC to exclude debris and doublets, followed by live cell selection using a viability dye. Monocytes were identified using a composite gating strategy: CD64⁺CD14⁺ and CD16⁺ cells were gated independently within live cells and then combined to define the total monocyte population. Monocyte subsets were classified as classical (CD14⁺⁺CD16⁻), intermediate (CD14⁺⁺CD16⁺), and non-classical (CD14⁺CD16⁺⁺). Expression of activation markers CD169, PD-L1, CD38, and HLA-DR was assessed within the total CD64⁺ monocyte gate.

Fig. 2

Hierarchical clustering of all biomarkers for no stimulation, on 40 patients (A), stimulation with immune complexes, on 40 patients (B), stimulation with LPS, on 35 patients (C) and stimulation with IFNα, on 38 patients (D). Levels are colored from low (dark blue) to high (dark red). C= child group, A= adult group, E= Elderly group.

Fig. 3

The median fluorescence of CD169, HLA-DR, CD38, CD16 and PD-L1 on total monocytes was measured in child, adult and elderly groups under the following experimental conditions: unstimulated, IFNα 400U/mL, LPS 500ng/mL, Ad5 (1000 particles per cell) + Immunoglobulins (2uL) (Ad5-IV/ICs), and Immunoglobulins alone (IV) (2uL). ****p < 0.0001; *p < 0.05; ns = not significant.

Fig. 4

The concentration of IFN-α, IFN-γ, IL1-α, IL1-RA, IL-2, IL-8, IL-10, IP-10 and TNF-α on monocytes’ culture supernatants was measured in child, adult and elderly groups under the following experimental conditions: unstimulated, IFN 400U/mL, LPS 500ng/mL, Ad5 (1000 particles per cell) + Immunoglobulins (2uL), and Immunoglobulins alone (2uL). ****p < 0.0001; *p < 0.05; ns = not significant.

Fig. 4

The concentration of IFN-α, IFN-γ, IL1-α, IL1-RA, IL-2, IL-8, IL-10, IP-10 and TNF-α on monocytes’ culture supernatants was measured in child, adult and elderly groups under the following experimental conditions: unstimulated, IFN 400U/mL, LPS 500ng/mL, Ad5 (1000 particles per cell) + Immunoglobulins (2uL), and Immunoglobulins alone (2uL). ****p < 0.0001; *p < 0.05; ns = not significant.

Fig. 5

Correlation table of monocyte activation in children (A), adults (B) and the elderly (C) during stimulation by immune complexes.

Fig. 6

Volcano plots of children versus elderly (A) of adult versus elderly (B), of children versus elderly (C) under stimulation with immune complex, Black circles are not significantly different between two groups. Data were z-scored prior to analysis.

Fig. 7

Monocyte activation profile during viral and bacterial infection and in the presence of immune complexes.

Fig. 8

Age-related differences in monocyte activation and its regulation.