Modulation of IL-6 production and IL-1 activity by keratinocyte-fibroblast interaction.
The present study was undertaken to investigate whether modulation of interleukin-6 and interleukin-1 production occurs owing to keratinocyte-fibroblast interaction. Normal human keratinocytes or squamous carcinoma cells were cultured either alone or in the presence of human foreskin fibroblasts or murine 3T3 cells. All cells tested produced interleukin-6, and interleukin-6 levels were markedly increased when normal or malignant keratinocytes were co-cultured with fibroblasts. The bioassay (species independent) and enzyme-linked immunosorbent assay (specific for human interleukin-6) together with use of complementary DNA probes specific for human or murine interleukin-6 revealed that fibroblasts are responsible for increased interleukin-6 levels. Moreover, interleukin-6 levels were increased when fibroblasts were cultured in conditioned media derived from normal human keratinocytes and squamous carcinoma cells-4 cultures. Interleukin-1 alpha secreted by normal human keratinocytes and squamous carcinoma cells-4 cells was mainly responsible for the increased interleukin-6 production in fibroblasts. Although interleukin-1 activity increased linearly with the incubation time in squamous carcinoma cells-4 monocultures, interleukin-1 activity was low and remained unchanged in squamous carcinoma cells-4/3T3 co-cultures. Low interleukin-1 activity was most probably not due to inhibition of interleukin-1 alpha production in squamous carcinoma cells-4/3T3 co-cultures because interleukin-1 alpha messenger RNA expression in squamous carcinoma cells-4 cells remained unchanged in the presence of 3T3 cells. Furthermore, when 3T3 cells were incubated in conditioned medium derived from squamous carcinoma cells-4 cells, high interleukin-1 activity decreased to an undetectable level, suggesting that fibroblasts are involved in the suppression of interleukin-1 activity. The remaining interleukin-1 activity, however, was sufficient for maximal induction of interleukin-6 production in fibroblasts. These results suggest that the interaction between epithelial and mesenchymal cells is at least partly initiated by interleukin-1 alpha secreted by the activated epithelial cell during skin injury or tumor invasion. Interleukin-1 in turn can induce modulation of the synthesis of various pro-inflammatory mediators and proteases in surrounding fibroblasts. An enhanced proteolytic activity and/or a possible induced production of an interleukin-1 inhibitor in fibroblasts and/or a receptor-mediated interleukin-1 consumption by fibroblasts will cause a decrease in interleukin-1 activity and thus exert a negative feedback.
Boxman
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I
Department of Dermatology, University Hospital Leiden, Amsterdam, The Netherlands.
Löwik
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C
Aarden
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L
Ponec
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M
D016475:3T3 Cells / Q000378:metabolism; D000818:Animals; D002450:Cell Communication; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000502:physiology*; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics; D015603:Keratinocytes / Q000166:cytology* / Q000378:metabolism; D008297:Male; D051379:Mice; D012333:RNA, Messenger / Q000032:analysis; D013997:Time Factors
D017077:Culture Media, Conditioned; D007375:Interleukin-1; D015850:Interleukin-6; D012333:RNA, Messenger