Dendritic cells are present in the lung in an immature state. Upon encounter with antigen or inflammatory stimuli, dendritic cells undergo maturation, a process associated with up-regulation of costimulatory molecules and secretion of IL-12. This process confers to the dendritic cell enhanced capacity to stimulate T cell responses. We speculated that cigarette smoking impairs the ability of dendritic cells to undergo maturation, thereby inhibiting their ability to stimulate T cell responses.
Immature dendritic cells were generated from monoyctes cultured with interleukin-4 (5ng/ml) and GM-CSF (800U/ml). Mature dendritic cells were generated by the addition of lipopolysaccharide (LPS, 100ng/ml) in the final 24 hours of culture. Cigarette smoke extract (CSE) was generated from cigarettes by bubbling mainstream cigarettes smoke from one cigarette into 10ml media (nicotine concentration of 2.3±0.8 microg/mL in 1% CSE). Costimulatory molecule expression was determined by flow cytometry. Dendritic cell interleukin-12 (IL-12) and interleukin-6 (IL-6) production were determined by ELISA.
Although CSE did not alter the expression of CD-40, CD-80, CD-86, and CD1a expression on resting immature dendritic cells, CSE (1-2%) caused significant suppression of LPS-induced upregulation of these co-stimulatory molecules. In contrast, nicotine (1-100 micrograms/ml) had no effect on resting or inducible co-stimulatory molecule expression. CSE also potently inhibited LPS-induced IL-12 secretion: whereas LPS-stimulated dendritic cells produced 1052 ± 9 pg/ml IL-12, LPS-stimulated dendritic cells in the presence of 2% CSE produced only 340 ± 9 pg/ml (p<0.01). In contrast to the suppressive effect on IL-12 secretion, CSE did not alter LPS-induced secretion of IL-6 by dendritic cells.CONCLUSIONS: These data indicate that CSE suppress specific dendritic cell functions that are important in host responses to infection and cancer. Through these effects on dendritic cell function, cigarette smoke components may alter adaptive immune responses.
These findings have important implications for the pathogenesis of disease states associated with smoking.
R. Vassallo, None.