Data from murine model of RA associated with a breach of self-tolerance brought some mechanistic explanations on this observation made in RA patients: abatacept is associated with a failure of T cells to acquire a follicular helper cell phenotype (CXCR5+ICOS+), to proliferate, to enter B cell follicles, leading to a reduction in antibodies responses (131). This evidence concerns the gene ICOS and rheumatoid arthritis.