Immunity to Litomosoides carinii in Mastomys natalensis. I. Effect of immunization with microfilariae and existing primary infections on the parasitaemia after microfilariae injection and challenge infection

A comprehensive, model-based review of vaccine and repeat infection trials for filariasis

SUMMARY Filarial worms cause highly morbid diseases such as elephantiasis and river blindness. Since the 1940s, researchers have conducted vaccine trials in 27 different animal models of filariasis. Although no vaccine trial in a permissive model of filariasis has provided sterilizing immunity, great strides have been made toward developing vaccines that could block transmission, decrease pathological sequelae, or decrease susceptibility to infection. In this review, we have organized, to the best of our ability, all published filaria vaccine trials and reviewed them in the context of the animal models used. Additionally, we provide information on the life cycle, disease phenotype, concomitant immunity, and natural immunity during primary and secondary infections for 24 different filaria models.

Immunoepidemiology of Wuchereria bancrofti infection in two East African communities: antibodies to the microfilarial sheath and their role in regulating host microfilaraemia

The response pattern of specific antibodies to the microfilarial sheath (sheath-Ab) of the mosquito-borne filarial parasite Wuchereria bancrofti was investigated in individuals from two East African communities with different levels of endemicity. Individuals from both communities presented a strong inverse relationship between positivity for sheath-Ab and being positive for microfilariae (mf) and circulating filarial antigens (CFA). The prevalence of sheath-Ab positivity was highest in young individuals, but peaked at a younger age in the high (1-14 years) than the low (15-19 years) endemicity community. IgG1, IgG2, IgG3 and IgE intensities to a crude adult filarial worm antigen were higher, and IgG4 intensities were lower, in sheath-Ab positive than in sheath-Ab negative individuals, probably reflecting the infection status of individuals. From the study it appears that individuals become sheath-Ab positive before mf and/or CFA can be detected in the peripheral blood, and only after later disappearance of sheath-Ab from the circulation can CFA and mf be diagnosed. In light of the findings, possible roles of the distinct sheath-Ab in the host-parasite relationship are discussed, and a hypothesis is proposed which suggests that sheath-Ab play an important role in the regulation of host microfilaraemia.

Surface antigens of Litomosoides carinii microfilariae: agglutinating antibodies react with sheath components of 40 and 120 kilo Dalton molecular mass

This study was conducted to identify surface antigens of the microfilarial sheath of Litomosoides carinii which are accessible to antibodies. Rabbit antisera were raised against the soluble and insoluble fractions of purified sheaths by extracting them with a buffer containing 2-mercaptoethanol and sodium dodecylsulphate. These sera and rabbit hyperimmune sera directed against homogenates of total microfilariae, mature (i.e. microfilariae liberating) female parasites and excretory-secretory products of adult females were able to agglutinate live and formaldehyde-fixed microfilariae. When the antisera directed against sheath constituents were administered to patently infected Mastomys coucha, the microfilaraemia of these animals was rapidly reduced and remained low for a period of 2-3 weeks. Antibodies specifically binding to the microfilarial surface were immunoaffinity-purified on formaldehyde-fixed microfilariae. The antibodies react with sheath antigens of 40 and 120 kDa molecular mass which are produced by the epithelium of the distal uterus of the mature female, secreted and attached to the surface of the sheaths. A 120 kDa antigen recognized by anti-sheath surface antibodies was also detected in the excretory-secretory products of in vitro-cultured immature female L. carinii from day 30 post-infection onwards. In the excretory-secretory products of mature adult female parasites recovered on day 130 post-infection, this 120 kDa molecule was absent. However, material reacting with the antibody was detected in the stacking gel of SDS-polyacrylamide gels. This finding may indicate that the basic units forming the 120 kDa antigen of immature adults or microfilarial sheath surface antigens occur in a highly polymerized form in the excretory-secretory products of mature female parasites.

Immunity to Litomosoides carinii in Mastomys natalensis. II. Effects of chemotherapeutically abbreviated and postpatent primary infections on challenges with various stages of the parasite

Naive Mastomys natalensis, Litomosoides carinii-infected M. natalensis at a postpatent stage of the infection and L. carinii-infected M. natalensis treated chemotherapeutically with furazolidone (FUR), FUR and diethylcarbamazine (FUR/DEC) or amoscanate (AMOS) were challenged by either injection or implantation of 40 third stage larvae (L3, s.c.), 40 fourth stage larvae (L4, 16 days old, i.p.), 20 male and 20 female preadult worms (36 days old, i.p.), 12 adult female worms (i.p.) or 6 X 10(6) microfilariae/kg (i.v.). Microfilaraemia in animals challenged at a postpatent stage (independent of the kind of challenge), was either totally suppressed or at least greatly reduced. Necropsy of L3-challenged animals showed that neither the length of the worms nor their content of morphologically intact, intrauterine stages was affected. Infected, treated animals challenged with developing stages (L3, L4 and preadult worms) showed reduced levels of microfilaraemia (by up to 75%). Dissection of AMOS-treated, L3-challenged animals showed that both the developmental rate and the fertility of the worms were affected. Microfilaraemia was also reduced after implantation of adult worms into treated animals. This was independent of the interval between treatment and challenge (44-150 days) except in animals challenged 10 days after AMOS-treatment, which showed no difference from naive controls. However, infected, treated M. natalensis, cotton rats and gerbils did not develop immunity against intravenously injected blood microfilariae.