Interestingly, P3, who displayed the most severe disease, presented with the highest titers and neutralizing activity of anti-GM-CSF auto-Abs. Immune responses to mycobacteria are controlled principally by IFN-γ, as demonstrated by findings for patients carrying mutations of any of the 20 genes leading to MSMD [9, 10]. Here, IFNG is linked to Mendelian susceptibility to mycobacterial diseases.