Effect of Mycobacterium vaccae on cytokine responses in children with atopic dermatitis

The increasing prevalence of atopic diseases over the last few decades is thought to be due to reduced exposure to environmental microbes that normally down-regulate allergic responses (hygiene hypothesis). We have shown previously that administration of the environmental microbe Mycobacterium vaccae ameliorates atopic dermatitis in school-age children at 3 months post-treatment. The present study tested the hypothesis that M. vaccae suppresses Th2-type cytokine activity and increases transforming growth factor (TGF)-beta(1) immunomodulatory activity in these children. Interleukin (IL)-4, IL-5, TGF-beta(1) and interferon (IFN)-gamma activity were assessed in resting and stimulated peripheral blood mononuclear cells (PBMC) isolated from 12 of the children who received M. vaccae in our original clinical trial. A cDNA expression array was used to examine a broader range of cytokine pathway transcripts. There were no significant changes in either Th2-type or TGF-beta(1) activity. A 5- to 10-fold increase in Th1-type activity was found at 1 month post-M. vaccae administration (P < 0.05), but it had returned to baseline by 3 months. The results do not support the hypothesis that M. vaccae reduces Th2-type or increases TGF-beta(1) activity of PBMC isolated from children with atopic dermatitis. The transient surge in IFN-gamma at 1 month is unlikely to explain any improvement in eczema score at 3 months.