Parasite-specific antibody and cellular immune responses in humans infected with Necator americanus and Oesophagostomum bifurcum

In this study parasite-specific antibody, cellular reactivity and Th1-type or Th2-type cytokine responses were investigated in humans concurrently inf ected with Necator americanus and Oesophagostomum bifurcum. The prospects f or O. bifurcum-specific serodiagnosis based on IgG4 and IgE were evaluated. IgG4 showed low specificity for O. bifurcum due to antigen cross-reactivit y with N. americanus, while IgE specifically distinguished between hookworm and O. bifurcum, and, in doubly infected patients, levels of O. bifurcum-s pecific as well as N. americanus-specific IgE were significantly elevated c ompared to those with N. americanus mono-infections. Cellular immunity was not strictly dominated by a Th1- or Th2- type reactivity. In co-infected pa tients cellular unresponsiveness to parasite antigens was observed, while c ellular production of tumour necrosis factor alpha (TNF-alpha) and gamma-in terferon (IFN-gamma) was greater in those doubly infected. Th2-type cytokin es (interleukin-5 and interleukin-10) were produced in equal amounts by per ipheral blood mononuclear cells from individuals with mono- and coinfection s. Such mixed Th1-type and Th2-type immune responsiveness associated with p ersisting gastrointestinal parasitic nematodes may reflect a state of infec tion at which parasite-induced inflammatory and enteropathogenic responses co-exist, and furthermore, helminth coinfection will not only suppress para site-specific cellular responsiveness but may also direct cytokine producti on towards a "permissive Th1-type cytokine profile" that favours parasite p ersistence.