Increased levels of soluble interleukin-4 receptor in the sera of patientswith visceral leishmaniasis

Kenyan subjects with visceral leishmaniasis were examined for evidence of i ncreased production of soluble interleukin-4 receptor (sIL-4R), Soluble IL- 4R regulates the bioactivity of IL-4, a cytokine important in mediating pro gressive forms of leishmaniasis. Persons with visceral leishmaniasis sustai ned 8- to 10-fold more circulating sIL-4R compared with Papua New Guinea re sidents with documented filariasis or uninfected Kenyan and North American subjects. Soluble IL-2R concentrations were elevated nonspecifically in bot h visceral leishmaniasis and filariasis patients, These findings are signif icant given that IL-4 induces sIL-4R in mice, and treatment with recombinan t sIL-4R cures progressive murine leishmaniasis dependent on IL-4 bioactivi ty, Further studies are indicated to determine whether the immunologic dete ction of IL-4 produced in human visceral leishmaniasis is obscured because of sequestration by soluble receptor and whether the production of sIL-4R i s relevant to the pathogenesis of visceral leishmaniasis.