IL21 and Fever: • Leukopenia• Neutropenia• Lymphopenia• Thrombocytopenia• Fever• Development of acute eosinophilic pneumonia• Elevated BDNF levels only in relapsing males• Increase in IL–6, TNF-α, and CRP levels (rats)• Decreased IL-1β, IL-6, IL-8, MIP-1β, fraktaline, TNF-α, IL-7, IL-13 IL-17a, IL-23, IL-21, IL-4, IL-10, eotaxin, and MCP-1 levels.• Increase in IL-10, IL-RA, and TNF-α levels.• Increase in Igγ chain levels.• Decrease in titers of platelet-associated antibodies titers.• Reduced platelet aggregation.• Reduction in IFN-γ production and Th1 differentiation by PBMCs.