IL21 and Respiratory tract infection: Combined with bioinformatics analysis, we established an IL-21R-deficient (IL-21R−/−) mouse model of Chlamydia muridarum (C. muridarum) respiratory tract infection in vivo, studied C. muridarum-stimulated RAW264.7 by the addition of rmIL-21 in vitro, and conducted adoptive transfer experiments to clarify the association between IL-21/IL-21R and Mφ.