The Role of Anaphylatoxin During in Vitro Anaphylaxis

Treatment of fresh normal rat plasma with a high molecular weight polysaccharide, Zymosan, activates a potent histamine liberator presumeably identical with anaphylatoxin. Under controlled conditions, the in vitro anaphylactic response of actively sensitized guinea pig ileum segments may be maintained unimpaired after rendering such tissue refractory to the immediate effects of rat anaphylatoxin. Conversely, desensitization of guinea pig ileum segments to specific antigen does not impair responsiveness to rat anaphylatoxin. These findings suggest that: a) specific antigen can release significant quantities of histamine from sensitized tissue without the intervention of circulating, surface absorbed, or cellular included anaphylatoxin; b) desensitization to multiple antigens such as exist in horse serum, or to anaphylatoxin, cannot be attributed simply to depletion of releaseable tissue histamine; and c) the point of attack of anaphylatoxin and of specific antigen upon sensitized cells is not identical. The results fail to support the “unified” concept of anaphylaxis suggesting that activation of serum anaphylatoxin constitutes a necessary intermediate step in the release of tissue histamine.