THE IMMUNE RESPONSIVENESS OF ROMNEY SHEEP SELECTED FOR RESISTANCE OR SUSCEPTIBILITY TO GASTROINTESTINAL NEMATODES - LYMPHOCYTE BLASTOGENIC ACTIVITY, EOSINOPHILIA AND TOTAL WHITE BLOOD-CELL COUNTS

Blastogenic activity, eosinophil and total white blood cell counts (TW BC) were examined over a period of 14 weeks in Romney lambs, genetical ly resistant or susceptible to gastrointestinal nematodes. The lambs w ere infected with 5000 infective Trichastrongylus colubriformis larvae twice weekly. Compared to preinfection levels, the blastogenic activi ty of unstimulated lymphocytes in lambs of both lines peaked at week 3 , and was significantly higher in resistant than in susceptible lambs. These changes may have been due to in vivo polyclonal activation, Lym phocytes from susceptible sheep responded more strongly to Con A, PHA and PWM than cells from resistant sheep. Counts per minute (c.p.m) for Con A- and PHA-stimulated lymphocytes increased in both lines of shee p from week 2 to week 7 and then returned to initial levels. An increa se in c.p.m. in PWM-stimulated cell cultures was observed from weeks 3 to 5 in both groups. The blastogenic activity for LPS-stimulated cult ures was significantly higher for resistant than susceptible sheep at weeks 3 and 4. No significant correlations between the decline in faec al egg counts (FEC) and the blastogenic activity was observed. Eosinop hil counts in peripheral blood began to increase one week earlier in r esistant than in susceptible sheep. No significant correlation between FEC and eosinophil counts was observed in resistant lambs, whereas in susceptible lambs a significant correlation was found between FEC and eosinophil counts at some sampling times. TWBC in resistant lambs ste adily increased with infections whereas susceptible lambs showed a dec rease until week 5 and then steadily increased, There was no significa nt correlation between the decline in FEC and TWBC. It was concluded t hat breeding for resistance or susceptibility to gastrointestinal nema tode infections influences selectively some parameters of the cellular immune response.