The CD 4+ cells through their T cell receptor-CD3 complex recognize the epitope-bound MHC II molecules on the surface of the antigen presenting cells, and get activated. Upon this activation, these T cells proliferate and differentiate into T1 or T2 cells. This makes them produce soluble chemical signals that promote their own survival. However, another important function that they carry out is the stimulation of B cell by establishing direct physical contact with them.