Validation of human IL-6 expression in knock-in mice. (A) RT-PCR analysis of human IL-6 (hIL-6) and mouse IL-6 (mIL-6) expression in different tissues of a Rag2^−/−Il2rg^−/−IL6^h/m mouse. mGAPDH served as an endogenous control. (B) RT-PCR analysis of mIL-6 and hIL-6 expression in thymus (left) and BM (right) of Rag2^−/−Il2rg^−/−IL-6^m/m, IL-6^m/h, and IL-6^h/h mice. (C) ELISA measurement of mouse (left) and human (right) IL-6 protein in plasma of non-engrafted IL-6^m/m or IL-6^h/h mice after LPS challenge (in ng/mL, n = 3). Each dot represents 1 mouse. Horizontal bars indicate mean values.