In Section 1, various methods employed for the quantification of IgE are discussed, and detailed accounts are given of the techniques used in this laboratory. Total IgE levels in human sera have been estimated using the Phadebas radioimmunosorbent test (RIST). This is a competitive radioimmunoassay in which IgE in a sample competes with radiolabelled IgE for sites on sephadex-anti-IgE particles. The usefulness and limitations of the test are discussed. A rat radioimmunosorbent test (RIST), and the Rowe modification of the Mancini single radial diffusion test are both described in detail. Both tests measure total IgE levels in rat sera. The rat RIST is a direct 'sandwich' radioimmunoassay in which IgE in a sample binds to anti rat IgE bound to activated paper discs. Finally addition of radiolabelled anti-rat IgE acts as a marker for the amount of sample IgE bound, RIST is more sensitive than the Rowe-Mancini test, detecting IgE levels as low as 10ng/ml. Technical aspects of the tests are discussed in detail. Antigen specific rat IgE is measured by the radio allergo-sorbent (RAST) and passive cutaneous anaphylaxis (PCA) tests. The RAST is based on the same principle as the rat RIST, but antigen instead of anti-IgE is bound to activated paper discs. The RAST has been used in this laboratory to detect IgE directed against egg albumin and N. brasiliensis antigens, and of the two systems the egg albumin RAST is the more efficient, N. brasiliensis / RASTS Radio allergosorbent tests being hampered by lack of pure antigen preparations. The RAST was found to be only partially reproducible, but extremely sensitive. The PCA test is the test of choice in this laboratory for the quantification of antigen specific IgE, and is discussed in detail in this section. Section III presents a study of the relationship in time between the elevation of total serum IgE, the parasite-specific IgE response, and the potentiated IgE response to unrelated antigen which occurs in rats following infection with the worm parasite N. brasiliensis. During a first infection the potentiated IgE response (to egg albumin) and elevation of total IgE occur synchronously rising to a peak on days 12-14 after infection, with the fastest rate of increase occurring between days 8 and 10. N. brasiliensis-specific IgE rises to a peak some 2-3 weeks later when both total IgE and the potentiated response have largely declined. A strain difference is shown in that Wistar rats produce far lower levels of total and parasite-specific IgE than Hooded Listers. Events following reinfection differ in that total IgE rises more rapidly, very high levels being reached 6 days after reinfection together with a secondary specific IgE response to N. brasiliensis. The total IgE level, however, rises by a far greater factor than parasite-specific IgE and declines rapidly while the parasite-specific response declines slowly over many weeks. The egg albumin response is not repotentiated. It is proposed that the total IgE response and the potentiated IgE response which forms a small component of it results from the release of a non-specific IgE-stimulating factor produced by N. brasiliensis-specific T cells. In this scheme the same or similar cells are involved in the production of N. brasiliensis-specific IgE through a separate specific helper function. In Section II experiments were described in which primary and booster IgE antibody responses were elicited in Hooded Lister rats by the intradermal injection or oral administration of very small quantities of egg albumin. Oral immunization was effected by giving antigen by stomach tube or in the drinking water. The minimum primary dose of antigen found to be effective was I ug intradermally and 10 mug orally, administered together with an intraperitoneal injection of B. pertussis adjuvant. In rats immunized with these doses secondary responses could be evoked by giving even smaller quantities of antigen, thus 1 ng intradermally or 1 mug orally without adjuvant. Smaller challenge doses were not tried. Large primary doses of antigen (>100 mug) presented by these routes were, on the other hand, found to be inhibitory to the production of secondary IgE responses, this effect being similar to that observed in previously reported intraperitoneal immunization experiments. By contrast with previous experiments, however, tertiary responses could be obtained following immunization by these routes, and I believe this to be a reflection of the absorption of smaller and therefore less inhibitory quantities of antigen. The results are discussed in relation to the control of IgE antibody production, current concepts of the control of antigen absorption through mucosal barriers, and possible implications for the genesis of naturally occurring IgE responses in man
