Detection of a ∼100 kD protein with strong immunoreactivity to antibodies specific for inducible nitric oxide synthase (iNOS) but without NOS activity in neutrophils of patients suffering from sepsis:: Results of a preliminary study

Objective: The study was designed to evaluate the expression of inducible nitric oxide synthase (iNOS) in activated human neutrophils. Subjects and Methods: By Western blotting and immunocytochemical staining, iNOS expression was analyzed in neutrophils from patients with sepsis who we classified by high plasma nitrate as subjects with activated NO metabolism. For comparison, rats treated with Zymosan documented to induce iNOS were analyzed. Results: Strong immunoreactivity to antibodies for iNOS was detected in leukocytes of Zymosan treated rats and in neutrophils of septic patients. Such immunoreactivity was absent in untreated rats and healthy subjects. In rats, the immunoreactivity was associated to the 130 kD protein as expected for iNOS. In contrast, the intense iNOS staining in neutrophils of septic patients was associated to a similar to 100 kD protein. Despite the iNOS staining, no increased NOS activity could be demonstrated in the neutrophils of septic patients. Conclusions: The detection of a similar to 100 kD protein with immunoreactivity to antibodies recognizing human iNOS but without NOS activity in neutrophils of patients with sepsis should initiate studies to elucidate the origin and function of this protein.