BTN molecules show the structural and functional similarities to the B7 family of molecules. Btn2a2-/- mice were shown to have increased CD4+ T cell responses and resistance to tumors, stronger autoimmunity. In this thesis, firstly, it was discovered that marginal zone B cells express the highest levels of Btn2a2. Then, it was found that Th1 and Th2 CD4+ T cell responses are stronger in CD19-cre x Btn2a2flfl mice. CD8+ central memory T cells were found to be higher in both CD19-cre x Btn2a2flfl and Btn2a2-/- mice compared to CD19-cre and WT mice. BTN2A2 absence worsened the lupus symptoms in Btn2a2-/-Nba2.Yaa spontaneous disease model. From these data, the roles of BTN2A2 in B cells are elucidated and the most important immune cell types that are affected by the loss of BTN2A2 are concluded.