Immunity to onchocerca lienalis microfilariae in mice. I. Resistance induced by the homologous parasite.

The model of Onchocerca lienalis microfilariae injected into inbred CBA/HT6T6 mice has been examined for its value to study immunity to the skin-dwelling microfilariae in onchocerciasis. Mice injected with living microfilariae during primary or secondary infections exhibited a high level of resistance to challenge relative to normal controls (91-98% reduction in recoveries). The survival of microfilariae during a primary infection was significantly prolonged in T-cell deprived animals compared with immunologically intact mice. Serum and spleen cells transferred from donors 90 days after infection conferred significant protection in syngeneic recipients to challenge with microfilariae (59% reduction in recoveries compared with controls). Boostered injections with freeze-killed or fragmented microfilariae reduced parasite recoveries after challenge by 39-78%: none of 5 adjuvant preparations enhanced the protective effect. Mice exposed to living infective larvae or adult males of O. lienalis also exhibited lowered recoveries of microfilariae following a challenge infection. It is concluded that the mouse model offers potential for immunological studies on the microfilariae in onchocerciasis, which have hitherto been limited because of the lack of suitable laboratory hosts.