[Components of complement in patients with immediate hypersensitivity].

Background: This prospective study was undertaken to assess the differences between the levels of the main plasma components of complement in allergic subjects and in those with pseudoallergic clinical manifestations.

Methods: Plasma C3 and C4 were evaluated in a total of 256 subjects examined consecutively at the allergology outpatients clinic of the Internal Medicine Division B, University of Turin. Total IgE and C1-inhibitor levels were also determined in 128 and 44 subjects respectively.

Results: C3 and C4 levels were not significantly different (p = 0.398 and p = 0.497) in 123 subjects with a positive and 133 with a negative prick test, nor in allergic subjects with respiratory as opposed to skin symptoms (p = 0.293 and p = 0.462), whereas the C-1 inhibitor was significantly lower (p = 0.046) in the respiratory subgroup. Total IgE was positively correlated with the C3 level (p = 0.036) in 75 allergic subjects.

Conclusions: These findings suggest that plasma C3 and C4 values are not sufficient to discriminate IgE inflammation (positive prick test) and pseudoallergy (negative prick test) in the assessment of subjects with clinically suspected allergy. The positive correlation between IgE synthesis and C3 also points to an interaction between IgE synthesis and C3 regulation proteins in patients with IgE mediated diseases. Further investigation of other acute phase proteins (C reactive protein, fibrinogen) and the cytokines regulating their synthesis (IL-6) in such patients will help to clarify this correlation.