A method for determining whether the descending limb of a biphasic histamine release curve reflects insufficient cross-linking.

We introduce a kinetic method for determining whether the descending limb of a biphasic histamine release dose-response curve is the result of insufficient cross-linking, and delineate conditions under which it is applicable. The method involves examining kinetic curves showing for various fixed antigen concentrations the cumulative amount of histamine release as a function of time. From the slope of the kinetic curves measured at some fixed time one determines how the rate of release depends on concentration. We show under very general conditions that if the dose-response curve for histamine release reaches a peak, and then decreases over a concentration interval in which the rate of release does not decline, then the decline in the dose-response curve cannot be due to insufficient cross-linking. Consequently, a characteristic feature of antigen-excess inhibition of histamine release due to mechanisms other than insufficient cross-linking is the crossing of a kinetic curve generated at a suboptimal antigen concentration by a kinetic curve generated at a supraoptimal antigen concentration. We show that the technique is easily executed experimentally and provide kinetic evidence-suggesting that the rabbit basophils the antigen-excess inhibition of histamine release by bis-benzylpenicilloyl-1,6-diaminohexane (BPO2) is due to insufficient cross-linking, whereas the antigen-excess inhibition observed with ovalbumin probably is due to more complete desensitization mechanisms.