| Abstract: | Factors influencing lung IgA antibody responses to Nippostrongylus brasiliensis infections and the role of lung and fecal IgA antibodies in immunity to this nematode were studied in rats. Hooded Lister rats were vaccinated subcutaneously with infective larvae radio-attenuated at 80-180 kr or with a single dose of infective larvae somatic proteins administered intravenously or intragastrically, and then challenged 14 days later with normal larvae. It was found that optimal lung IgA antibody responses depended more on the duration of the antigenic stimulation than on the quantity of antigenic material present, although a threshold amount was required. However, comparisons of lung anti-larval IgA antibody levels in rats resistant or susceptible to challenge indicated that these antibodies were not directly involved in specific host protective immunity. Levels of haemagglutinating fecal antibodies reacting with adult nematode metabolites were correlated with the numbers of adult worms recovered from the intestines following vaccination and also with the degree of resistance to reinfection. However, preincubation of adult (day 5) nematodes in media containing the IgA fraction of fecal globulins from primary infected rats did not reduce the ability of these worms to establish and survive in naive rats. |
