LOCAL AND PLASMA ANTIBODY-RESPONSES TO THE PARASITIC LARVAL STAGES OFTHE ABOMASAL NEMATODE OSTERTAGIA-CIRCUMCINCTA

Ovine isotype-specific antibody responses to the parasitic larval stag es of the abomasal nematode Ostertagia circumcincta were measured in a simple, indirect enzyme-linked immunosorbent assay. Analysis of varia nce of replicate tests showed that the assay was very reliable. There was substantial variation among individual sheep in their IgA and IgG1 responses even though the sheep had been matched for breed, age and s ex, were born on the same farm, were reared identically and had the sa me history of exposure and challenge with O. circumcincta. The local I gA responses to a somatic extract of fourth-stage larvae were very sim ilar to responses to excretory-secretory products of fourth-stage larv ae. The responses to third stage larvae were correlated with the respo nses to fourth stage larvae. There was a negative correlation between parasite-specific plasma IgG1 and parasite-specific plasma IgA respons es. There was only a moderate association between IgA responses in the mucus and the plasma. Therefore, antibody responses measured in plasm a cannot be easily extrapolated to antibody responses in the abomasal mucus.