Beta-carotene in vitro stimulates tumor necrosis factor alpha and interleukin 1 alpha secretion by human peripheral blood mononuclear cells

Beta-carotene (BC) potentially affects cancer resistance by stimulating secretion of immunoregulatory cytokines and thereby modulating immune defenses. Therefore, we investigated the effects of BC applied in vitro on the secretion of interleukin-1 alpha (IL-1), tumor necrosis factor alpha (IL-1), tumor necrosis factor alpha (TNF) and interferon-gamma (IFN) by human peripheral blood mononuclear cells (PBMC). PBMC from healthy individuals were activated with pokeweed mitogen (PWM; 0.1 ug/ml), or lipopolysaccharide (LPS; 10 ug/ml) for 24 hr, or phytohemagglutinin (PHA; 5 ug/ml) for 74 hr. BC was encapsulated in liposomes and delivered to PBMC during mitogen activation at concentrations of 10^-6 to 10^-11M. The concentration of cytokines in the supernatants of activated cells was measured by ELISA. BC had no impact on IFN release. The release of IL-1 was significantly (p<0.05) stimulated by BC (10^-6 to 10^-8 M). No effect on IL-1 secretion was obtained when PBMC were incubated with BC-free liposomes. However, BC-free liposomes suppressed significantly TNF secretion (from 1.5 to 0.2 ng/ml). When BC was presented in liposomes at concentrations ranging from 10^-6 to 10^-8 M it stimulated significantly (p<0.01) TNF secretion. We suggest that physiologically achievable concentration so BC stimulate monokine secretion. Such changes might explain in part the observed immunomodulatory effect of BC on lymphoid cells and reduced cancer risk associated with high intake of BC.