SECRETION OF ANTIPARASITE SUBSTANCES AND LEUKOTRIENES FROM OVINE GASTROINTESTINAL TISSUES AND ISOLATED MUCOSAL MAST-CELLS

The presence of larval migration inhibitory (LMI) compounds in the gas trointestinal mucus of nematode resistant sheep has been shown previou sly to be associated with increased numbers of gastrointestinal mucosa l mast cells (MMC) and globule leukocytes (GL). This experiment was de signed to determine if LMI compounds were secreted by MMC/GL in respon se to nematode antigenic challenge and if so, could secretion account for levels observed in mucus. Romney sheep were immunized by repeated cycles of infection with Trichostrongylus colubriformis or Haemonclus cortortus larvae and anthelmintic treatment. After slaughter, gastroin testinal tissue was taken for examination of histology and mucus anti- parasite activity. Segments of small intestine were ligatured to form sacs which were incubated with exsheathed nematode larvae or larval ex cretory/secretory antigens. Tissue slices from small intestine or abom asum were also incubated with nematode larvae or antigens. After homol ogous challenge, levels of leukotrienes secreted into small intestinal tissue sacs were significantly higher than levels in heterologously c hallenged sacs or unimmunized sheep intestinal sacs challenged with la rvae of any nematode species (279.4 +/- 33.7, 141.0 +/- 27.8 and 39.5 +/- 15.2 ng h(-1) respectively). Tissue slices gave a similar pattern of leukotriene secretion. LMI activity was also significantly elevated in intestinal sacs from immunized sheep challenged homologously with nematode larvae or antigen (64 +/- 10 and 68 +/- 14% respectively cf. heterologous challenge 32 +/- 10% and unimmunized sheep sacs 15 +/- 6% ). Histological examination of abomasal and small intestinal sections showed that immunized sheep had significantly greater numbers of IMMC/ GL than unimmunized sheep. MMC/GL isolated and purified from immunized sheep secreted leukotrienes and compounds having LMI activity when cu ltured with homologous nematode larvae or antigens. Secretion of leuko trienes and molecules having LMI activity from MMC/GL could account fo r the levels of these substances observed in small intestinal mucus.