CaMK4 controls follicular helper T cell expansion and function during normal and autoimmune T-dependent B cell responses

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by dysregulated B cell compartment responsible for the production of autoantibodies. Here, we show that T cell-specific expression of calcium/calmodulin-dependent protein kinase IV (CaMK4) leads to T follicular helper (T(fh)) cells expansion in models of T-dependent immunization and autoimmunity. Mechanistically, CaMK4 controls the T(fh)-specific transcription factor B cell lymphoma 6 (Bcl6) at the transcriptional level through the cAMP responsive element modulator alpha (CREMalpha). In the absence of CaMK4 in T cells, germinal center formation and humoral immunity is impaired in immunized mice, resulting in reduced anti-dsDNA titres, as well as IgG and complement kidney deposition in the lupus-prone B6.lpr mouse. In human T(fh) cells, CaMK4 inhibition reduced BCL6 expression and IL-21 secretion ex vivo, resulting in impaired plasmablast formation and IgG production. In patients with SLE, CAMK4 mRNA levels in T(fh) cells correlated with those of BCL6. In conclusion, we identify CaMK4/CREMalpha as a driver of T cell-dependent B cell dysregulation in autoimmunity.