Sequestration of labelled granulocytes in the lungs following administration of OKT3 is dose-dependent.

In the present study the consequences of administration of low-dose (0.5 mg) OKT3 for respiratory side-effects and pulmonary sequestration of labelled granulocytes are compared with the known effects of 5 mg OKT3. Ten renal transplant patients were studied, of whom five were treated with 0.5 mg OKT3 and five with 5 mg OKT3. None of the patients in the 0.5 mg group and two of the patients in the 5 mg group experienced dyspnoea. Sequestration of labelled granulocytes in the lungs was significantly lower in the patients receiving 0.5 mg OKT3 compared with the patients receiving 5 mg OKT3. The simultaneously occurring peripheral blood granulocytopenia was significantly more severe in the 5 mg group than in the 0.5 mg group. We suppose that this sequestration of circulating granulocytes in the lungs is at least partly mediated by complement activation products. In vitro it is demonstrated that fixation of complement activation products on peripheral blood lymphocytes depends on the concentration of OKT3 present in the culture medium. We conclude that respiratory side-effects shortly following infusion of OKT3 are related to complement-induced pulmonary leucostasis, the degree of which is dependent on the administered dose of OKT3.