The induction of antibody production by IL-6 is indirectly mediated by IL-21 produced by CD4+ T cells.
Dienz O, Eaton SM, Bond JP, Neveu W, Moquin D, Noubade R, Briso EM, Charland C, Leonard WJ, Ciliberto G, Teuscher C, Haynes L, Rincon M. The induction of antibody production by IL-6 is indirectly mediated by IL-21 produced by CD4+ T cells. J Exp Med. 2009 Jan 16; 206(1):69-78.