Cellular responses to Loa loa experimental infection in mandrills (Mandrillus sphinx) vaccinated with irradiated infective larvae

In order to shed light on the mechanisms of antifilarial protective immunit y, we investigated the course of experimental loaiosis after vaccination in a nonhuman primate host, Mandrillus sphinx. Six vaccinated (V) mandrills r eceived 50 irradiated L3 while six nonvaccinated (NV) received saline solut ion on days -60, -30 and -15. All animals were challenged with 100 intact L 3 (day 0). Parasitological and immunological status were followed for 9 mon ths. Vaccination delayed the appearance and mean peak of microfilaraemia. F ive mandrills (Mf-) were never microfilaraemic (one V mandrill) or microfil araemic on only one occasion (2 V and 2 NV), the other seven having stable microfilaraemia (Mf+). The cytokine response of peripheral blood mononuclea r cells to L3 (L3 Ag) was Th2 dominated, while microfilariae (Mf Ag) elicit ed a Th0-like response. During vaccination, Th2 cytokine production signifi cantly increased in V mandrills against L3 Ag, as well as Mf Ag, whereas Th 1 cytokines decreased. On day 60 postinoculation, cellular proliferation wa s higher in V mandrills in response to L3 and Mf Ags and PHA-L mitogen. At the end of prepatency (on day 130), mandrills with delayed appearance of mi crofilaraemia exhibited a high, transient IL-2 and IL-4 secretion in respon se to L3 Ag. Finally, high anti-Mf Th2 cytokine levels characterized Mf-man drills not only during prepatency, but also (for IL-5) before immunization. However, the presence of a balanced Th1 anti-L3 response during prepatency in the amicrofilaraemic mandrill suggests its importance in protective imm unity. Taken together, our data suggest that Th2 cells and also Th1 compone nts of the antifilarial response, especially to larval antigen, may contrib ute to parasite elimination.