Trichinella spiralis: genetic basis and kinetics of the anti-encysted muscle larval response in miniature swine.

Primary-infected swine lymphocyte antigen (SLA) inbred miniature swine, NIH minipigs, of the SLAa/a haplotype (aa) display markedly reduced Trichinella spiralis-encysted muscle larval (ML) burdens 6 weeks after homologous challenge and are therefore referred to as responders against encysted T. spiralis ML. To investigate the kinetics and genetics of the anti-encysted ML response, and in an attempt to ascertain the mechanisms underlying this phenomenon, NIH minipigs of multiple SLA haplotypes, designated either as ax (aa, ac, ad, af, ag, dh and hh) or non-ax (cc, cd, and dd), received a primary inoculation of 300 T. spiralis ML followed by a challenge inoculation of 10,000 ML 6 or 17 weeks later. Pigs were examined at necropsy and at Weeks 1, 2, 3.5, and 6 after challenge. Statistical cluster analyses, based on final ML burdens, performed on 129 pigs in 13 trials, revealed that 47% of primary-plus-challenged ax pigs exhibited responder phenotype as early as 1-2 weeks after T. spiralis challenge whereas this response was manifested in only 8% of non-ax pigs. No correlation was observed between responder phenotype and T. spiralis-specific blastogenesis, cell expression of class I or class II SLA molecules, lymphoid cell subsets, adult worm numbers, or fecundity. Although some ax responder pigs exhibited a localized inflammatory response with a prominent eosinophilic infiltrate surrounding degenerating encysted ML, no correlation was observed between responder phenotype and either peripheral blood eosinophilia or the ability of eosinophil-enriched cell populations from responder pigs to adhere to or destroy encysted ML in vitro.