['Transitional cell carcinoma (TCC) of the bladder is associated with alterations in the immune system of the host. The authors demonstrated that in patients with bladder carcinoma there is a negative correlation between the levels of natural killer (NK) activity and the clinical evolution and pathologic stages of disease.', 'The authors investigated the effect of various doses of recombinant interferon-alpha-2b (IFN-alpha-2b) for variable periods of culture on the nonmajor histocompatibility-restricted cytotoxic activity of peripheral blood mononuclear cells (PBMNC) with or without CD16 and CD3-depleted populations from patients with superficial (confined to the mucosa or lamina propria) and infiltrative (those infiltrating beyond the lamina propria) TCC of the bladder using 4-hour 51-sodium chromate (51Cr)-release cytotoxicity assays against both NK-sensitive (K562) and NK-resistant (JY) tumor target cells.', 'The normal NK activity detected in PBMNC from patients with superficial TCC of the bladder can be significantly enhanced by short-term (18-hour) incubation with recombinant IFN-alpha (P < 0.05). The depressed NK cytotoxic activity found in PBMNC from patients with infiltrative TCC can also be significantly enhanced, but not normalized, by short-term (18-hour) incubation with recombinant IFN-alpha (P < 0.05). Short-term recombinant IFN-alpha-incubated PBMNC from patients with superficial, but not infiltrative, TCC of the bladder also showed marked cytotoxic activity against NK-resistant target cells. By selection with CD16 or CD3 monoclonal antibodies and complement, it was also found that the precursor and effector lymphocytes of this recombinant IFN-alpha-promoted cytotoxicity belong to NK lineage. In kinetic studies, it was found that the maximal levels of the recombinant IFN-alpha-promoted cytotoxic activity against NK-sensitive and NK-resistant target cells in PBMNC from patients with TCC were reached after 18 hours of culture.'] Does interferon-alpha-2b enhance the natural killer activity of patients with transitional cell carcinoma of the bladder?