ABSTRACT. Bernardo A.R., da Rocha J.D.B., de Lima M.E.F., Decote-Ricardo D., Pinto-da-Silva L.H., Peçanha L.M.T. & Danelli M. dasG.M. Modulating effect of the piperine, the main alkaloid from Piper nigrum Linn., on murine B lymphocyte function. [Efeito modulador da piperina, principal alcalóide da Piper nigrum Linn., sobre a função de linfócitos B murinos.] Revista Brasileira de Medicina Veterinária, 37(3):209-216, 2015. Departamento de Microbiologia e Imunologia Veterinária, Instituto de Veterinária, Universidade Federal Rural de Janeiro, Campus Seropédica, BR 465 Km 7, Seropédica, RJ 23890-000, Brazil. E-mail: danelli @ufrrj.br Piperine is the main alkaloid of black and long peppers and it is conventionally used as immune-enhancers in Indian system of traditional medicine. The main of this study was evaluated for the first time the effect of piperine on B cells functions in vitro and its effects on humoral immune response to T-dependent and T-independent antigens. Different concentrations of piperine (1 µM, 3 µM and 15 µM) were assayed on B cells purified from BALB/c spleen cells and evaluated its effects on proliferation, IgM secretion and expression of CD86 on murine B cells. At 15 µM piperine was able to inhibit the proliferative response induced by LPS and α-IgM antibody and inhibited the secretion IgM antibody in vitro. Also, piperine at 3 µM and 15 µM reduced the CD86 expression on B cells stimulated with LPS and α-IgM antibody in vitro. However, piperine 2.5 and 4.5 mg/Kg did not modulated antibody production for T-independet (TNP-Ficoll) in vivo.