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Experiments are described which demonstrate that a single intraperitoneal (i.p.) injection of antigen in Freund's complete adjuvant results in the appearance of IgA-specific antibody-containing cells (ACC) in the intestinal lamina propria of sheep and that these cells reach the intestine via the intestinal lymph and blood circulation. Following intraintestinal administration of antigen to sheep immunized i.p. 2 weeks previously, an enhanced ACC response occurs in the intestine but cannulation and drainage of the intestinal duct does not interfere with this enhancement. Evidence is presented which suggests that the enhanced ACC response may be accounted for by antigen-induced local proliferation of ACC in the lamina propria of the intestine.

Experiments were carried out to determine the effect of a range of adjuvants on the antibody response of sheep to a subcutaneous injection of ovalbumin. Incomplete Freund's adjuvant (IFA) was the best of the repository type adjuvants. From a range of soluble immunopotentiating substances tested, the polyion DEAE-dextran, or dextran sulphate, produced the greatest enhancement of the response. These results were confirmed in a factorial experiment, but no interactions were found between various classes of adjuvants. Further experiments were carried out to determine the effect of superior adjuvants, prior immunization or intradermal injection on the rate and mode of uptake of antigen from the injection site to afferent lymph. These experiments showed that, with IFA, most antigen is retained at the injection site, less than 15% entering lymph by 3 days. There was some delay in antigen uptake with adjuvant 65, while for aluminium phosphate precipitated antigen, the rate of uptake was the same as following a saline injection. There was some delay in uptake of antigen following injection with DEAE-dextran or in primed sheep but, following intradermal injection, the rate of uptake into lymph was the same as aqueous antigen injected subcutaneously. Experiments in which the distribution of radioactive antigen between cells and plasma in lymph was examined showed that, in unprimed sheep, virtually all antigen is unassociated with cells. In primed sheep, however, about 0.5% of antigen in lymph was found to be cell-associated. Gel filtration of lymph plasma from primed sheep demonstrated that nearly all the antigen in lymph is carried to the node as high molecular weight material, presumably antigen-antibody complexes.

The aim of the present study was to develop an immunization procedure which centrally stimulated the IgA system of sheep with the release of antibody-containing cells (ACC) of the IgA class into intestinal lymph. It was found that intraperitoneal injection of ovalbumin resulted in a substantial output of ACC in intestinal lymph. ACC of the IgA class reached a peak 8--9 days after intraperitoneal injection when they comprised 1.4% of cells in lymph. ACC of the IgM and IgG1 classes comprised 3.5 and 2.9% of cells in lymph at this time. The output of ACC of the IgA, IgM and IgG1 classes in lymph at the peak of the response was respectively, 3.7 X 10(6), 9.8 X 10(6) and 8 X 10(6) cells/h. In marked contrast to rats, virtually no ACC appeared in intestinal lymph of sheep following intraduodenal infusion of ovalbumin in animals primed 2 weeks earlier by intraperitoneal injection of antigen in Freund's complete adjuvant (CFA).

The output and immunoglobulin class of antibody-containing cells (ACC) in lymph from different regions of adult sheep has been compared following intraperitoneal or subcutaneous injection of ovalbumin in Freund's complete adjuvant (FCA). Intraperitoneal injection of antigen in FCA elicited no response at all in popliteal lymph, but there were substantial responses in lymph from the hepatic, coeliac (which carries lymph mainly from the abomasum and anterior duodenum) and intestinal lymphatic ducts. A significant increase in the number of blast cells accompanied the ACC response. ACC reached a peak 7- days after injection when ACC comprised 3.7% +/- 0.7%, 2.3% +/- 0.7% and 3.3% +/- 0.6% of total lymphocytes in lymph from the hepatic, coeliac and intestinal ducts respectively. At this time ACC were distributed among three immunoglobulin classes IgM, IgG1 and IgA with the latter constituting 25%--40% of ACC in lymph from the three regions. ACC did not appear in intestinal lymph following subcutaneous injection of ovalbumin in FCA in the leg immediately below the tarsus. This contrasted with the vigorous response in popliteal lymph where 6 days after the injection ACC constituted 3.9% of cells in lymph. Most (83%) of the ACC were IgG1-specific at the peak of the response. The remaining ACC were distributed among the IgM, IgG2 and IgA classes with the latter comprising 3% of total ACC.