Mechanisms for monocyte activation in co-culture with autologous tumor spheroids

Biopsies from carcinoma tissue and benign control mucosa from head and neck squamous cell carcinoma patients were used to establish fragment (F)-spheroids in vitro. We have previously shown that autologous monocytes co-cultured with F-spheroids in vitro secrete interleukin (IL)-6 upon 24 h in co-culture. Presently, the aim was to study the mechanisms of this monocyte secretion. Paraformaldehyde (0.1% for 2 min) or actinomycin-D (1 μg/ml for 24 h) pre-treatment of the F-spheroids abolished the monocyte IL-6 co-culture response. Addition of glucose (100 mM) or mannose (100 mM), and to some extent galactose (100 mM), but not fructose (100 mM) to the co-cultures, partly inhibited the monocyte IL-6 co-culture response, but such addition did not inhibit the in vitro monocyte lipopolysaccharide (LPS)-generated IL-6 secretion. When mannose was added to the co-cultures, monocyte IL-6 mRNA expression was eradicated in malignant co-cultures and reduced to a low level in benign co-cultures. Addition of mouse anti-human β1-integrin (anti-CD29) antibody (2 μg/ml) diminished the IL-6 co-culture response but not the monocyte LPS-generated IL-6 response. In conclusion, the monocyte IL-6 co-culture response is dependent on live spheroids and to some extent on direct contact with the F-spheroids, possibly via lectin-like receptor(s), the mannose receptor and β1-integrin.