Schwerd et al. report a novel homozygous missense substitution in the cytokine co-receptor GP130 encoded by IL6ST. This is associated with defective IL-6, IL-11, OSM, and IL-27 signaling and causes immunodeficiency and skeletal abnormalities with similarities to STAT3 hyper-IgE syndrome. Here, IL11 is linked to immunodeficiency disease.