The role of IgG1 hypergammaglobulinaemia in immunity to the gastrointestinal nematode Nematospiroides dubius. The immunochemical purification, antigen-specificity and in vivo anti-parasite effect of IgG1 from immune serum

Nematospiroides dubius, in common with many other species of metazoan parasite, induces an IgG1 hypergammaglobulinaemia during the course of infection. In the present study, immune sera raised in CFLP mice by repeated infection contained 24 ng/ml IgG1 compared with a resting level of 2.4 mg/ml. IgG2a and IgG2b levels were depressed following infection from 1.5 to 0.6 mg/ml and 0.64 to 0.42 mg/ml respectively. IgM levels were unaltered by infection (0.16 mg/ml) whilst IgA levels increased from 0.7 to 1.2 mg/ml. Immunochemical fractionation of immune sera by a combination of affinity chromatography and gel filtration revealed that the anti-parasite activity of the original serum could be largely accounted for by purified IgG1 fractions as assessed by immunoprecipitin and immunofluorescence assays. Purified IgG1 was shown to react with antigenic components common to both adult homogenate and adult excretory-secretory antigen. In addition, absorption studies revealed that as much as 48% of purified IgG1 from immune serum reacted with adult N. dubius antigen. In vivo, IgG1 was the only purified immunoglobulin isotype to cause significant reduction in worm numbers in the gastrointestinal tract when administered alone, and to have any noticeable co-operative effect when administered in conjunction with immune mesenteric lymph node cells. IgG1 also caused severe stunting of worms, and promoted the adherence of peritoneal exudate cells to the worm surface in vitro. It is suggested that one mechanism by which immune mesenteric lymph-node cells exert their protective activity following cell transfer is by elevating IgG1 levels in recipient mice.