Synthesis of complement components C3 and factor B in human keratinocytes is differentially regulated by cytokines

The complement system plays an important part in host defense and inflammat ion. Locally synthesized complement may perform these functions at tissue a nd organ level. In skin the keratinocyte is the major cell type, it is know n to produce two soluble complement components, C3 and factor B. In this st udy we investigated the regulation of synthesis of these components in fore skin keratinocytes by cytokines. Human keratinocytes were cultured in the p resence of supernatant of activated peripheral blood mononuclear cells, int erleukin-1 alpha, interleukin-2, interleukin-6, transforming growth factor- beta 1, tumor necrosis factor-alpha, or interferon-gamma. C3 and factor B p roteins were measured in culture supernatant by enzyme-linked immunosorbent assay and C3 and factor B transcripts in harvested cells by reverse transc riptase-polymerase chain reaction. Cultured keratinocytes constitutively pr oduced C3 and factor B. Supernatant of activated mononuclear cells upregula ted C3 and factor B production by 27- and 15-fold, respectively. interleuki n-1 alpha, interferon-gamma, and tumor necrosis factor-alpha upregulated C3 synthesis by 7-, 8-, and 22-fold, and interleukin-1 alpha, interleukin-6, and interferon-gamma upregulated factor B synthesis by 3-, 3-, and 34-fold, respectively. Tumor necrosis factor-alpha induced production of C3 and int erferon-gamma induced production of factor B were inhibited by cycloheximid e. Cytokine induced upregulation of C3 and factor B proteins was always ass ociated with the upregulation of levels of C3 and factor B mRNA. This indic ated that, as expected, cytokine-induced enhancement in C3 and factor B lev els was due to an increase in synthesis rather than their possible release from intracellular stores. In conclusion, synthesis of C3 and factor B in k eratinocytes is regulated by some cytokines, known to be produced by inflam matory cells and keratinocytes.