Immunity and leg ulcers in homozygous sickle cell disease.

Probably because of an abnormality of the alternative pathway of complement activation, acute bacterial infections are common in patients with homozygous sickle cell (SS) disease. To find out whether defective immunity might also predispose to chronic bacterial infection, SS patients with indolent ulcers of the legs were studied. When compared with SS individuals who had never had ulcers the differences of serum immunoglobulin and complement component concentration were similar to those found in a comparison of ulcer patients with normal (AA) haemoglobin genotype and AA controls. Both ulcer groups had higher than normal prevalences of serum cryoprecipitates and anticomplementary activity. However, the latter was found less commonly in SS patients than AA patients, suggesting that SS patients form immune complexes which lack the ability to fix complement. They may therefore have a defect of immune elimination which could predispose to chronicity of infection even in the presence of an adequate antibody response.