Transfer of immunity to the microfilariae of Onchocerca lienalis in mice

The model of Onchocerca lienalis microfilariae (mf) in CBA mice has been employed to examine the immunological mechanisms underlying the destruction of skin-dwelling mf in immunised hosts. Spleen cells from highly resistant donors transferred to naive, syngeneic recipients conferred significant protection against mf challenge, with up to 78% reductions in parasite recoveries. Levels of resistance afforded by adoptive transfers of immune cells were dose dependent and only significant above a threshold of 4 x 10(6) splenocytes. Mixed T and B lymphocytes elicited resistance in recipients, although neither cell population was protective alone. Immune serum evoked resistance to mf challenge by passive transfer, but only when collected shortly after booster immunisations of the donors. Xenogeneic sera from immunised rabbits or calves failed to confer protection to recipient mice. It is concluded that resistance to O. lienalis mf in mice is likely to be primarily governed by a thymus-dependent humoral response.