Tocilizumab, a humanized anti-IL6R monoclonal Ab of the IgG1 class is widely used to treat rheumatoid arthritis [26], Castleman’s Disease [27],amyloid A amyloidosis [28], etc. IL6 is considered to be an important biomarker for novel SARS-CoV2 infection [29,30] and anti-IL6 treatment are currently under trials [31,32]. Here, IL6 is linked to Castleman disease.