HIGM1 patients are highly susceptible to infections caused by opportunistic pathogens such as Pneumocystis jirovecii (Levy et al, 1997; Winkelstein et al, 2003), whose effective clearance requires CD4 T cell‐dependent activation of both B cells and macrophages (Otieno‐Odhiambo et al, 2019). This evidence concerns the gene CD4 and infection.