Markers of Loa loa infection in permanent residents of a loiasis endemic area of Gabon

Different markers of infection were analysed in 56 permanent residents of a Loa loa endemic village in Gabon. The population was divided into those with parasitological evidence of L. loa infection and those with no history of loiasis over the period of observation (c. 5 years). 26·7% of villagers had L. loa microfilariae, 33·9% had an ocular passage of an adult worm, and 17·8% had calabar oedema. Several other clinical symptoms were present in both groups of individuals, but none was considered to be pathognomonic for L. loa infection. Most of the villagers were polyparasitized, with Plasmodium falciparum and gastrointestinal parasites being particularly prevalent. Mansonella perstans was present in 80% of the villagers and was equally distributed between L. loa microfilaraemic and amicrofilaraemic individuals. Eosinophil levels were elevated in the whole population, and were not significantly different between the groups who were infected and non-infected with L. loa. Polyclonal immunoglobulin (Ig) E levels were high in both the Ambinda villagers and in Gambian serum from patients infected with M. perstans alone and there was no significant difference between the levels of L. loa specific IgG in the Ambinda villagers and the Gambian patients. However, the level of L. loa specific IgG4 was elevated in 75·6% of amicrofilaraemic individuals and could discriminate between most individuals infected with L. loa and those infected with M. perstans, suggesting that this is the best determinant of infection status in the absence of L. loa microfilariae

IgG subclass recognition of Loa loa antigens and their correlation with clinical status in individuals from Gabon

In endemic areas for Loa loa, a significant percentage of actively infected individuals have no circulating microfilariae, an observation which implies the existence of a stage-specific immune response. In an attempt to define the immunological basis of the amicrofilaraemic state, the reactivity of antigens from adult, microfilariae and infective larvae of L. loa was examined by Western blotting with individual serum samples from four clinically defined groups (high microfilaraemic, low microfilaraemic, amicrofilaraemic and endemic controls) using IgG subclass-specific reagents and IgE. In the adult parasite, a complex of antigens at 28-31 kDa was exclusively recognized by IgG1 from amicrofilaraemic individuals and, to a lesser extent, by IgG1 from endemic controls. However, this complex of antigens was recognized by IgG4 antibodies in serum samples from all individuals, including microfilaraemics. A microfilarial antigen of 21 kDa was recognized by IgG1 antibodies present in serum from amicrofilaraemic, endemic control and low microfilaraemic individuals. Persons with high levels of microfilariae did not recognise this antigen. In both the L3 and the microfilariae, a ladder antigen with increments of 15 kDa was the main target of IgG4 antibodies in amicrofilaraemic and microfilaraemic individuals. IgE antibodies recognized more antigens in the microfilarial stage than in the adult of L3. These results suggest that immunological differences between clinically defined groups are associated with the recognition of different antigens or epitopes

High levels of parasite-specific IgG4 in the absence of microfilaremia in Loa loa infection

The specificity of IgG4 as marker of infection has been investigated. The study was based on two well defined clinical groups: amicrofilaremic individuals with verified ocular passage of adult worms of Loa loa, and microfilaremic patients. Both groups were compared to Africans not exposed to loiasis infection and to Europeans. The study revealed that there is no significant difference in the level of parasite-specific IgG4 between individuals with occult infection (i.e. amicrofilaraemic, but infected) and microfilaremic individuals, but there is a significant difference between L. loa infected individuals and Mansonella perstans exposed people. IgG4 of individuals exposed to L. loa infection recognised specific antigens in the molecular weight range 12-30 kDa. We conclude that the elevated level of filarial-specific IgG4 is therefore not dependent upon the presence of circulating microfilariae and that serology using homologous L. loa low molecular weight antigens, can facilitate specific diagnosis of occult loiasis in an endemic area with mixed filarial infections

Parasitological and immunological effects induced by immunization of

Six mandrills were immunized with 150 Loa loa infective stage larvae (L3) irradiated with 40 Krad, and challenged with 100 L3, 60 days after initial vaccination. The parasitological outcome of this immunization was compared to results from six mandrills infected with normal L3. No clear association was seen between vaccination and microfilaremia until day 245 when a significant drop in the level of microfilaria occured in vaccinated compared to infected animals (5 vs 10 mf/ml; p = 0.012). A one-year follow-up of the humoral immune response showed a strong adult, microfilariae (Mf) and L3 specific IgG response, with distinct profiles for each extract. In immunized animal a significant decrease in antibody level was systematically observed between days 90-145 for the anti-L3 and anti-adult IgG. However, in the same group anti-Mf antibody levels that peaked around 160-175 days post-challenge, were inversely correlated with the decrease in Mf density between day 200 and day 386. These results suggest that immunization with irradiated L3 using these specific conditions may affect the appearance of Mf

Parasitological and immunological effects induced by immunization of Mandrillus sphinx against the human filarial Loa loa using infective stage larvae irradiated at 40 krad

Six mandrills were immunized with 150 Loa loa infective stage larvae (L3) irradiated with 40 Krad, and challenged with 100 L3, 60 days after initial vaccination. The parasitological outcome of this immunization was compared to results from six mandrills infected with normal L3. No clear association was seen between vaccination and microfilaremia until day 245 when a significant drop in the level of microfilaria occured in vaccinated compared to infected animals (5 vs 10 mf/ml; p = 0.012). A one-year follow-up of the humoral immune response showed a strong adult, microfilariae (Mf) and L3 specific IgG response, with distinct profiles for each extract. In immunized animal a significant decrease in antibody level was systematically observed between days 90-145 for the anti-L3 and anti-adult IgG. However, in the same group anti-Mf antibody levels that peaked around 160-175 days post-challenge, were inversely correlated with the decrease in Mf density between day 200 and day 386. These results suggest that immunization with irradiated L3 using these specific conditions may affect the appearance of Mf