GM-CSF level were increased in serum (106 pg/ml, normal < 6 pg/ml) of the child and normal in the parents. No anti-GM-CSF autoantibodies were detected in serum [19] . GM-CSF-Ra chain expression after stimulation with 50 ng/ml GM-CSF on peripheral mononuclear cells of the patient was markedly reduced and normal in both parents ( Figure 6C ). In the absence of GM-CSF stimulation, GM-CSF-Ra chain in the parents was only 50% of that of the controls ( Figure 7A ), whereas GM-CSF-Rb chain and CD11b were normal. After stimulation with GM-CSF, GM-CSF-Ra and CD11b remained low in the patient ( Figure 7A, lower panel) , whereas the parents' levels were in the normal range level. GM-CSF-Rb chain without and with GM-CSF stimulation was normal ( Figure 7A ). CD11b expression on the neutrophils was used to assess signal transduction after GM-CSF stimulation. In the patient, similar as blocked by auto-antibodies from a subject with auto-immune PAP, no dose-dependent stimulation of CD11b was observed, demonstrating interruption of signalling ( Figure 7B ).