In vitro parasite antigen-induced antibody responses in human helminth infections

Helminth parasites characteristically induce vigorous antibody responses in human infections, but the immunoregulatory mechanisms determining the level of these responses are not at all understood. To investigate these mechanisms, peripheral blood mononuclear cells were obtained from 10 patients with parasitic helminth infections (three with schistosomiasis, three with onchocerciasis, and four with loiasis), along with six normal controls. These cells were then cultured in vitro and the capacity of the cells to respond to a specific parasite antigenic stimulus was examined by measuring the amount of parasite-specific antibody produced. Parasite antigen alone, without exogenous mitogen, induced an IgG anti-parasite antibody response in vitro. Optimal responses were obtained at extremely low antigen concentrations--concentrations at which little if any polyclonal immunoglobulin production occurred. Additionally, the in vitro induction of parasite-specific antibody was antigen dose-dependent, requiring much lower antigen concentrations than those necessary to induce lymphocyte blastogenesis. Antibody production was shown to require the cooperative interaction of B and T cells. These studies demonstrate that in vitro responses to antigens from naturally acquired parasitic infections, like those in individuals postimmunization, can be utilized to dissect the cellular and humoral factors that regulate antibody production to naturally acquired human pathogens.