Deficiency of the second component of complement associated with anaphylactoid purpura and presence of mycoplasma in the serum.

A patient, with deficiency of the second component of complement (C2), who has had anaphylactoid purpura for 12 years is described. Other classical complement components were present normally and the very markedly low total haemolytic complement activity was restored by the addition of functionally purified C2. Glycine-rich β-glycoprotein (GBG), measured antigenically, was reduced to about 50% of normal but the alternate pathway to complement activation was normal as judged by the platelet factor three activation test. Structures identified morphologically as mycoplasma were present in the patient's serum.