We previously reported that about 80 % of patients with
atopic dermatitis and 60 % with
cholinergic urticaria revealed type I
allergy against sweat, by means of skin test against autologous sweat and/or histamine-release test for peripheral blood basophils with semi-purified sweat
antigen. In this study, we developed an assay for sera to neutralize
histamine-releasing activity of semi-purified sweat
antigen. The semi-purified sweat
antigen was pre-incubated with serially diluted sera for 30 min at 37 °C and was subjected to histamine-release activity. Histamine release-neutralization (HRN) activities were calculated by measuring the amount of histamine release from basophils in the presence or absence of semi-purified sweat
antigen. Of 62 subjects, 39 showed positive histamine release (≥5 %) from their basophils in response to semi-purified sweat
antigen, and sera of 34 out of 39 subjects (87.2 %) were also positive in HRN activity (≥10 %). The specificity of the HRN assay was 0.522. Moreover, HRN activities in sera were largely correlated with degrees of histamine release from peripheral blood basophils of the same donors in response to sweat
antigen. To identify the substance that neutralizes histamine-release activity, we removed
IgE and
IgG from the sera of HRN (+) subjects by column chromatography. The HRN activities in 30 out of 42 sera were largely reduced by the removal of
IgG. On the other hand, sera of four subjects lost HRN activity by the removal of
IgE, suggesting that the majority of HRN (+) subjects have serum
IgG against the sweat
antigen as well as
IgE bound to peripheral basophils. Thus, the HRN assay maybe useful for the screening of type I
allergy against sweat
antigen.