THE SENSITIZATION OF MUCOSAL MAST-CELLS DURING INFECTIONS WITH TRICHOSTRONGYLUS-COLUBRIFORMIS OR HAEMONCHUS-CONTORTUS IN SHEEP

Responses of isolated mucosal mast cells (MMC) during infections with either Trichostrongylus colubriformis or Haemonchus contortus were exa mined by measuring the release of sheep mast cell protease (SMCP) in a degranulation assay. MMC from sheep immune to T. colubriformis releas ed maximal amounts of SMCP and histamine within 0.5h of incubation wit h larval antigen whereas maximum secretion of leukotrienes occurred 3h after addition of antigen. It was only after 8 weeks of a primary T. colubriformis infection, that MMC released significantly elevated leve ls of SMCP (23%); this occurred when the worm burden was being rejecte d. In contrast, the SMCP release from MMC of immune sheep was signific antly higher at 40%, and occurred within 1-4 days after challenge (DAC ). The SMCP release peaked at 6-8 DAC at 51%, and declined after 56 DA C to <25%. MMC isolated from the duodenum and mid-small intestine of i mmune sheep released 2-3 times higher proportion of SMCP than did cell s recovered from the terminal ileum. Mast cell numbers were similar in the 3 regions but the quantity of globule leucocytes (GL) was 2.5 tim es higher in the duodenum. During infections with H. contortus in the abomasum, MMC isolated from the small intestine released greater level s of SMCP when incubated with larval antigens than did abomasal MMC. T here was no increased release during the first 12 weeks of a primary i nfection although the SMCP release (23%) from immune MMC at 7-10 DAC w as significantly enhanced. Once again the release from MMC isolated fr om the three intestinal regions of sheep immune to H. contortus was lo west in the terminal ileum. Mast cell numbers were 2 and 3 times highe r in the abomasum and duodenum than at the 2 distal sites and a signif icant number of GL was found only in the abomasum. The results suggest that the sensitization of MMC to parasite antigen during primary infe ction is closely associated with the development of acquired immunity to either parasite. The response is disseminated throughout the small intestine, and the high levels of SMCP release and number of GL at the site of parasitism probably reflect the greater sensitization of MMC in those region.