Temporal changes in the humoral immune response of cattle during experimental infections with Onchocerca lienalis

In order to gain insights into the immune response in onchocerciasis during early infection, laboratory-reared calves were infected with 1000 Onchocerca lienalis infective larvae and examined serologically over a period of 508 days. Levels of serum antibodies measured by ELISA against adult worm extract revealed a multiphasic response, characterized by a broadly similar profile of peaks in individual animals arising at 15-30, 79 and > 266 days after infection. Timings of these changes in responsiveness closely mirrored parasite development, coinciding with larval moults and with the onset of a patent infection. The levels of individual antibody isotypes directed against parasite antigens was strongly skewed. The dominant response was of IgG1, although limited reactivities were also found for IgG2 and IgM: No parasite-specific IgA antibodies were detected. Immunoblots of adult worms extracts revealed a pattern of antigen recognition over time that matched the results obtained by ELISA. Again, the IgG1 response was strongest, although certain IgG2 and IgM specificities were well represented. In general, there was a steady increase in the number of individual antigens recognized as the infection progressed, with a striking expansion of antibody specificities from day 79 following the fourth larval moult. Antibodies to a 16kDa component were a prominent feature of the response following development of a patent infection. These data reveal the strong influence of parasite biology on the development of the immune response in onchocerciasis.