Effect of minocycline and doxycycline on IgE responses

Background: We have recently found that the tetracycline minocycline suppresses inflammatory responses in serum immunoglobulin (Ig)E-positive asthmatic patients, and that IgE levels can decrease in these patients. The mechanism by which minocycline suppresses these responses is unknown. Objective: We have now investigated the ability of the tetracyclines, minocycline and doxycycline, to regulate IgE responses of peripheral blood mononuclear cells (PBMC) obtained from serum IgE-positive asthmatic patients. Methods: The distributions of CD3+, CD4+, CD8+, and CD19+ lymphocytes in peripheral blood of serum IgE-positive asthmatic patients and IgE-negative nonasthmatic controls, and cytokine-specific mRNA expression by their PBMC were determined by flow cytometry (reverse transcriptase-polymerase chain reaction). Serum Ig levels also were determined (nephelometry, fluoroenzymeimmunoassay, enzyme-linked immunoadsorbent assay; n = 7/group). PBMC (1.5 × 10⁶/mL) were cultured with anti-CD40 monoclonal antibody and recombinant human interleukin-4 in the presence/absence of minocycline or doxycycline (0.1 to 10 μg/mL), and IgE levels in supernatants determined on days 0, 3, and 10 (enzyme-linked immunoadsorbent assay). Results: Asthmatic and nonasthmatic subjects had similar numbers of blood CD4+ T cells (779/mm³ ± 73 and 766 ± 115, respectively) and CD19+ B-cells (239/mm³ ± 35 and 379 ± 95, respectively); however, CD8+ T cell numbers were decreased in asthmatic compared with nonasthmatic subjects (378/mm³ ± 66 and 568 ± 53, respectively; P = 0.045). High IgE levels were detected in supernatants of asthmatic PBMC on day 10 (28 ng/mL ± 12), whereas control IgE levels did not change (<2.5 ng/mL). When either minocycline or doxycycline was included in culture, IgE production by asthmatic PBMC was strongly suppressed in dose-dependent fashion on day 10 (>80% with 10 μg/mL); control IgE did not change (<2.5 ng/mL). Conclusions: The results are consistent with the idea that the therapeutic benefits obtained by asthmatic patients from minocycline may, in part, result from IgE suppression.