Specific antibody responses in rats and mice after daily immunization without adjuvant.

Abstract

We have previously devised an immunization protocol to obtain IgE antibody formation in mice without the use of adjuvants. In this communication the observations were confirmed using several antigens and various routes of administration. The studies were also extended to rats. Subcutaneous (s.c.) administration to rats of 100-ng doses of trinitrophenylated human serum albumin (TNP-HSA) in 10-day periods resulted in production of IgE antibodies as determined with the RAST using antirat IgE. Higher antigen doses resulted in lower IgE antibody responses. Intranasal (i.n.) or peroral (p.o.) exposure of rats did not result in any IgE antibody responses. Exposure to antigen by the s.c. and i.n. route but not p.o. administration induced IgG, IgM and IgA antibody responses in rats as recorded with the enzyme-linked imunosorbent assay (ELISA). Several different antigens were given to CBA/Ca mice, i.e. penicilloylated bovine gammaglobulin (PO-BGG), FITC-conjugated dog serum albumin (FITC-DSA) or timothy pollen extract. All the antigens induced boosterable IgE antibody responses as determined with RAST utilizing antimouse IgE. Antibodies of IgG isotype were also recorded after such immunizations, whereas only low IgM and no IgA antibody titers were found in serum employing ELISA. After similar daily administration of antigen by the p.o. or i.n. route of antigen at doses from 10<sup>2</sup> to 10<sup>5</sup> ng, IgG antibody responses but no IgE antibodies were found. Intranasal administration of 10<sup>6</sup> ng induced some IgE and IgA antibodies. A single p.o. administration of 4 × 10<sup>7</sup> ng of antigen induced an antibody response of the IgG class. Pretreatment of animals with 4 × 10<sup>7</sup> ng of PO-BGG orally prior to the 10-day periods of s.c. injections suppressed the IgE antibody responses by 80% but enhanced the IgG antibody response. It was concluded that IgE antibody responses can be induced in rats and mice by daily s.c. administration of small doses of a variety of antigens without the use of any adjuvants. Antibody responses of the other isotypes may also be raised by such immunization. Intranasal and p.o. administration is less efficient in this respect, possibly requiring much higher antigen doses. The protocol for s.c. immunization appears to be suitable for studies of the regulation of an allergic immune response.