Differential gene expression and functional responses in peripheral blood mononuclear cells pretreated with combustible and non-combustible tobacco products
Chronic smoking is known to alter immune responses, which compromises tumor surveillance and host defense against microbial infections. We previously showed that smokers (SMK) exhibit distinct peripheral blood mononuclear cell (PBMC) gene expression patterns relative to moist snuff consumers (MSC) and non-tobacco consumers (NTC). Moreover, exposure of PBMCs to cigarette whole smoke-conditioned medium (WS-CM) has been shown to suppress the expression of genes involved in inflammatory signaling pathways. We investigated whether PBMCs pre-treated with WS-CM or smokeless tobacco extract (STE) could activate signaling pathways in response to lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA)/ionomycin stimulation. Genome-wide expression was measured in PBMCs pre-treated for 3 hours with non-cytotoxic doses of WS-CM (low, medium and high doses) or STE (single dose); WS-CM and STE dosing was based on equi-nicotine units. Pre-treated cells were stimulated with LPS and PMA/ionomycin for 5 hours. The pre-treatment with STE and the low dose of WS-CM did not significantly alter the stimulated gene expression. However, cells pre-treated with the medium or high dose of WS-CM demonstrated many significant changes in LPS- and PMA/ionomycin-stimulated gene expression compared to un-treated cells. These changes were mostly a downregulation, indicating immune response suppression. The suppressive effects of WS-CM on inflammatory pathway-relevant gene expression persisted for over 24 hours, as evidenced by decreased levels of IFNɣ, TNFα and IL-2 in stimulated cells. Pathway analysis also revealed that even after pro-inflammatory stimulation, higher doses of WS-CM continued to suppress many signaling pathways associated with immune cell differentiation and inflammatory responses. Our results provide a mechanistic understanding of how tobacco smoking, rather than smokeless tobacco use, compromises immune function, rendering SMK to be more susceptible for certain diseases.