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The titer of anti-Culex quinquefasciatus antibodies which were mostly of IgG and IgE isotypes was determined in humans living in Wuchereria bancrofti endemic regions. A progressive increase in the titer of antibodies was observed with age. In contrast, sera from people living in regions where the Cx. quinquefasciatus is of low prevalence were found to have markedly reduced IgG and almost zero IgE levels.

Circulating antigens, antibodies to somatic and sheath components of microfilariae (mf) and immune complexes were determined in parallel in different categories of Wuchereia bancrofti infection using, respectively, reverse indirect haemagglutination (RIHA), indirect haemagglutination (IHA), indirect immunofluorescent (IFA) and polyethylene glycol (PEG) precipitation assays. Rabbit hyperimmune anti-W. bancrofti mf serum and mf homogenates were used as reagents. Appreciable levels of antigens and antibodies were detected in all categories; endemic normals, asymptomatic carriers, acute and chronic filarial cases. For example, even amongst endemic normals, i.e. those with neither clinical nor parasitological evidence of infection, 66%, 71% and 74% had mf antigens, anti-mf antibodies and anti-sheath antibodies, respectively. Notably, only a small proportion (9.4%) of microfilaraemic individuals had detectable level of anti-sheath antibodies. The relationship of these parameters with the spectrum of filariasis is discussed.

Antiserum was raised in rabbits against p-aminophenyl 2-acetamido-2-deoxy-beta-D-glucoside covalently coupled to phosphatidylaminoethanol-containing lecithin liposomes. The affinity-purified antibodies were found to be IgM. The properties of the antibodies were studied by ligand inhibition of quantitative precipitation, fluorescence titration with 2-acetamido-2-deoxy-D-glucose, and complement lysis of haptenated liposomes.

The binding of Fab mu of rabbit anti-galactocerebroside antibody to antigen incorporated in unilamellar liposomes has been investigated by fluorescence and circular dichroism measurements. The fluorescence intensity of Fab mu is found to be quenched considerably in the presence of liposomes concomitant with a blue-shift of the emission maximum. It is inferred from circular dichroism studies that there are changes in the aromatic residues and the disulfides as well as in the folding of peptide backbone of Fab mu. The results suggest that antigen-associated liposomal membrane induces changes in both the tertiary and the secondary structure of Fab mu.