Human Lung Carcinoma Cells Directly Interact with Monocytes in- vitro to Trigger Robust Release of TNF-α from Monocytes and Autocrine IL-6 Secretion

Inflammation is increasingly being associated with cancer initiation andprogression. Inflammatory mediators, mostly cytokines like TNF-α and IL-6, originate typically from tumor-immune cell interactions. Monocytes, precursors of macrophages, form a major chunk of the immune cells infiltrating the tumors and potential source of inflammatory signals. Devising in-vitro models to study he role of inflammatory mediators in human tumorigenesis, especially in challenging tumors like that of the lung, is a thrust area. In this study, we mimic in-vivo conditions, where lung carcinoma cells would come directly in contact with monocytes, by co- culturing representative human lung carcinoma cell line, A549 with human monocytic cell line, THP-1and evaluate TNF-α and IL-6 expression by immunoassays. TNF-α was detectable in co-culture supernatants as early as 1 hour after co-culturing of two cell types. Following the kinetics of TNF- α expression in the co-culture we observe that TNF-α levels reach to peak levels at 4-6 hours after co-culture before receding to lower levels indicating tight regulation of TNF-α expression. Surprisingly, high amounts of IL-6 were detected in the co-culture, even though THP-1 poorly expresses IL-6 unless pre-activated. We found IL-6 was almost exclusively coming from A549 cells, as only IL-6 of human origin was detected when A549 cells were co-cultured with mouse macrophages, RAW 264.7. The presence of TNF-α and IL-6 even after prolonged co-culture points to desirable presence of TNF-α and IL-6 for tumor cells. These results indicatethat tumor cells are able to interact directly with monocytes generating TNF-α in a regulated manner. This suggests a significant role of varying TNF- α and IL-6 levels in tumor microenvironment during tumorigenesis and in better understanding of inflammatory mechanisms associated with cancer.