<prompt> A possible source of second signal to a B-cell bound by specific antigen include -EB virusEndotoxinAntigen-specific T-cellsPlasma cells  <response>: Role of T cell in antibody formation:Antigen with class II MHC on antigen presenting cells activates the CD4 helper T cells. CD4 helper T cells produce cytokines that stimulate B cells which have already exposed to similar antigen.Though antibody is produced by B cells after differentiating into plasma cells, coordination of helper CD 4 T cells is also necessary.In antibody formation, T cells are involved earlier than B cells.After antigen exposure, antigen presenting cells present antigen to CD 4 helper T cells, which then secrete cytokines that induce differentiation of B cells which have already been exposed to the same antigen to plasma cells.Plasma cells form an antibody against that specific antigen. 