Studies on the allergenic significance and structure of rat serum albumin.

Abstract

This study evaluated the capacity of rat serum albumin and of its proteolytic fragments to activate human basophils for IgE-mediated histamine release. The leukocytes from 8 out of 33 patients allergic to rats released histamine with rat serum albumin. Two proteolytic fragments of rat serum albumin, each constituting half of the molecule, were used to study the IgE-reactive antigenic sites. These fragments released histamine with the cells of some of the donors, thus demonstrating the presence of at least 2 antigenic determinants on each fragment for a total minimum of 4 sites on the intact rat serum albumin molecule. Most of the allergenic activity, however, was not recovered in the 2 fragments (total recovery mean = 6.4%, range between 0.1 and 31%). This loss could be due to cleavage of the rat albumin molecule in the middle of the third domain with loss of antigenic sites and/or due to minor conformational changes in the fragments as compared with the intact molecule. There was up to a 500-fold difference in the percent of activity recovered in the fragments when tested on cells from different patients. Therefore, there is no single immunodominant site on the molecule equally important for all patients. The cells of all 8 patients also reacted with mouse serum albumin but only 2 with bovine serum albumin. At least 1 determinant on mouse and rat serum albumin is cross-reactive with IgE.