Since mast cells and basophils are thought to play a central role in several types of cutaneous inflammatory and allergic reactions, and since interleukin-6 (IL-6) is an important mediator in these processes, we have studied the ability of the human mast cell line HMC-1, the human basophilic cell line KU812, and human skin mast cells to produce IL-6. All three cell types proved to be potent sources of this cytokine after appropriate stimulation. Transcription of IL-6 mRNA was first detectable 2 h after stimulation with the ester phorbol myristate acetate (PMA) and the calcium ionophore A23187 in both cell lines, as evidenced by semiquantitative reverse transcriptase polymerase chain reaction analysis. Whereas resting cells did not produce IL-6 protein, PMA/A23187-stimulated cells released immunoreactive and biologically active IL-6, as demonstrated and quantitated by enzyme-linked immunosorbent assay and by the use of TEPC 1033 cells, an IL-6-dependent murine plasmacytoma cell line. Stimulated KU812 cells secreted sevenfold more IL-6 (up to 15 ng/ml) than HMC-1 cells (up to 2.4 ng/ml). Immunoblotting of HMC-1- and KU812 cell-derived IL-6 revealed several IL-6 forms in the molecular weight range of 21 to 30 kDa. Immunoelectron microscopic studies of human skin biopsies provided evidence that unstimulated mast cells do not contain preformed IL-6 but accumulate IL-6 in cytoplasmic and extruded granules after IgE-dependent stimulation. These findings suggest that IL-6 secreted by human mast cells and basophils potentially contributes to allergic, other immunologically mediated and nonspecific inflammatory responses.

Enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescent-antibody assay (IFA), and Western immunoblot were used to test serum samples from 128 dogs for the presence of antibody to Borrelia burgdorferi. Sera included 72 samples from dogs suspected of having Lyme disease, 32 samples from dogs residing in areas in which Lyme disease was not considered endemic, and 24 samples from dogs with clinical and serologic evidence of immune-mediated disease (n = 10), Rocky Mountain spotted fever (n = 5), or leptospirosis (n = 9). Results of Western immunoblotting were used as the standard against which performances of ELISA and IFA were measured. ELISA was significantly more sensitive than IFA (84.8 versus 66.7%), although both tests were equally specific (93.5%). Eight samples that were positive by Western immunoblot were simultaneously negative by ELISA and IFA. Of these eight, four were from dogs suspected of having immune-mediated disease, two were from dogs suspected of having leptospirosis, and two were from dogs suspected of having Lyme disease. These results may indicate that sera from dogs with immune-mediated disease, and to a lesser extent sera from those with leptospirosis, cross-react with B. burgdorferi antigens. Alternatively, Western immunoblot results may not truly reflect Lyme disease status, particularly in the case of dogs with immune-mediated diseases. At present, however, the use of Western immunoblotting as a diagnostic standard for dogs offers the best alternative to a clinical definition of disease.

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