CHANGES IN INFLAMMATORY MEDIATORS AND LARVAL INHIBITORY ACTIVITY IN INTESTINAL CONTENTS AND MUCUS DURING PRIMARY AND CHALLENGE INFECTIONS OF SHEEP WITH TRICHOSTRONGYLUS-COLUBRIFORMIS

Helminthologically naive merino sheep were given either a single infec tion of 30,000 or a trickle infection of 6000 Trichostrongylus colubri formis infective larvae (TcL3) per week. Faecal egg counts started to fall after 8 weeks in the single infection and after 11 weeks in the t rickle infection. Small intestinal contents were collected from indwel ling intestinal fistulae over the next 14 weeks. Concentrations of she ep mast cell protease (SMCP) in these contents increased to highest le vels 9-11 weeks and 6-10 weeks after the single infection and from the start of the trickle infection, respectively. Similarly, peptidyl leu kotriene (PLT) concentrations were highest at 6 weeks and at 6-9 and 1 3 weeks, respectively. Histamine concentrations increased slightly aft er both infections to peak values at 7 weeks and 9 weeks, respectively . Inhibition of migration of larvae in vitro was increased in contents sampled at 8 weeks after the single infection and after 6-10 weeks of the trickle infection. Another 2 groups of sheep were immunised by re peated infections with TcL3. Gut contents from 1 group sampled immedia tely before and after challenge with 30,000 TcL3 at 0 and 18 days had increased levels of larval migration inhibitory (LMI) activity through out the 35 day period, especially 7-14 days after challenge (DAC). The mediators SMCP increased significantly 5-7 DAC while PLT increased 7- 14 DAC. In the second group of immunised sheep, levels of SMCP and PLT increased rapidly within 1 DAC and further increased 3-14 DAC. Increa sed concentrations of platelet activating factor PAF occurred only at 14 DAC, while LMI activity was greatest in mucus collected 5-8 DAC. Si nce increased concentrations of these mediators occurred around the ti me when egg counts started to decline in primary infections and were i ncreased after challenge of immune sheep, the results suggest roles fo r the mediators and/or their cellular source in the expression of immu nity.