In a model of protective immunity against Onchocerca microfilariae (mf), it has been demonstrated previously that immunocompetent mice clear a primary
infection and are highly resistant to
re-infection. This immunity correlates with CD4+ Th2 cells, is dependent on
IL-5 but not
IL-4, and can be transferred adoptively with spleen cells. In the current investigation, high levels of spontaneous proliferation and of IFN gamma production were observed in splenocyte cultures from immune mice, compared with cells from naive controls.
Antigen-specific proliferation also occurred in immune cells, being vigorous following stimulation with adult worm
antigen, but not with
antigens from developing embryos or mf. Levels of
IL-4,
IL-5 and IFN gamma induced by the various
antigens was similar, indicating that activation of alternate T helper cell sub-sets was unlikely to explain the lack of cellular responsiveness. After a primary inoculation with mf, spleen cells from infected mice co-produced IFN gamma and
IL-5. In contrast, IFN gamma production was downregulated while
IL-5 levels remained high during active elimination of a challenge
infection. Significant levels of
IL-4 production occurred only once parasite clearance had begun. These data confirm the importance of
IL-5 in protection against Onchocerca mf in mice and question the role of IFN gamma in the expression of immunity. Production of high levels of
IL-5 correlated with blood and tissue eosinophil mobilization during the clearance of a challenge
infection.