Increased serum IgE levels are found in atopic diseases, especially atopic dermatitis. It is generally accepted that the high serum IgE levels are increased by exposure to exogenous antigens. However, exposure to antigens in the absence of proper adjuvants does not usually increase serum IgE. Here, we studied the involvement of skin factor(s) in increasing serum IgE. The soluble fractions were obtained from two keratinocyte cell lines, PAM 212 and KCMH-1, derived from BALB/c and CBA/J mice, respectively. These were injected subcutaneously into parental mice strains at 2-week intervals. The levels of serum immunoglobulins and the release of IgE in vitro from spleen cells were measured by ELISA. The biological activity of the increased serum IgE was assessed by sensitization of RBL-2H3 mast cells with serum. Six injections of PAM 212-derived fraction (PAM extract) consistently increased the serum levels of IgE, IgG1 and IgG2b, but not those of IgM, IgG2a, IgG3 or IgA in BALB/c mice. The high serum levels of IgE were sustained for at least 10 weeks after one or two injections of PAM extract. When RBL-2H3 cells were sensitized with the serum from mice injected with PAM extract, they released histamine in response to anti-IgE. Moreover, spleen cells of these mice produced significantly higher amounts of IgE than those of uninjected mice in the presence of IL-4 and anti-CD40 antibody. On the other hand, no significant increase in immunoglobulins was observed following injection of the soluble fraction from KCMH-1 cells in CBA/J mice. These results suggest that the release of the soluble fraction of keratinocytes and its exposure to immunologically competent cells may induce an increase in serum IgE levels by a Th2-dominant mechanism.

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