IMMUNOGLOBULIN METABOLISM IN SHEEP INFECTED WITH THE SMALL INTESTINAL NEMATODE TRICHOSTRONGYLUS COLUBRIFORMIS

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Abstract
Radiotracer techniques were used to compare the kinetics of IgG1 and IgG2 metabolism in sheep (1) prior to parasite exposure, (2) during an initial patent infection with Trichostrongylus colubriformis, and (3) during continuous exposure to the parasite when the animals were exhibiting resistance. Plasma concentrations of IgG1, IgG2, IgA and IgM were also monitored throughout the experiment. Plasma IgG1 concentration increased significantly during the development of resistance and maintained this higher level on further exposure to the parasite. IgA concentration was also elevated during the development of resistance to a level approximately three times that observed prior to initial infection, hut this increase was only transitory. No significant changes in either IgG2 or IgM concentration occurred. Analysis of the radiotracer data for IgG1 and IgG2, was based on a two-compartment model comprising intravascular and extravaseular protein pools with reversible exchange between them and irreversible loss from the intravascular site. No significant changes in compartment sizes or rates of exchange between compartments were recorded during measurement periods (1), (2) and (3) for either IgG1 or IgG2. Rates of irreversible loss of IgG2 were similar during (1), (2) and (3); the irreversible loss of IgG1 was unaltered following the initial infection but Increased by approximately 50% during period (3). It is concluded that increased synthesis of IgG1 in resistant sheep continually exposed to T. colubriformis occurs as a result of antigenic stimulation rather than as a consequence of increased loss of plasma into the intestine.